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A dog takes 4 leaps for every 5 leaps of a hare but 3 leaps of a dog are equal to 4 leaps of the hare. Compare their speeds. (M.B.A., 2007)
Let the distance covered in 1 leap of the dog be \(x\) and that covered in 1 leap of the hare be \(y\).
Then, \(3 x=4 y \Rightarrow x=\frac{4}{3} y \Rightarrow 4 x=\frac{16}{3} y\).
\(\therefore \quad\) Ratio of speeds of dog and hare
\(=\) Ratio of distances covered by them in the same time
\(
=4 x: 5 y=\frac{16}{3} y: 5 y=\frac{16}{3}: 5=16: 15 \text {. }
\)
While covering a distance of \(24 \mathrm{~km}\), a man noticed that after walking for 1 hour and 40 minutes, the distance covered by him was \(\frac{5}{7}\) of the remaining distance. What was his speed in metres per second?
Let the speed be \(x \mathrm{~km} / \mathrm{hr}\).
Then, distance covered in \(1 \mathrm{hr} .40 \mathrm{~min}\). i.e., \(1 \frac{2}{3} \mathrm{hrs}=\frac{5 x}{3} \mathrm{~km}\).
Remaining distance \(=\left(24-\frac{5 x}{3}\right) \mathrm{km}\).
\(
\begin{aligned}
\therefore \quad \frac{5 x}{3}=\frac{5}{7}\left(24-\frac{5 x}{3}\right) & \Leftrightarrow \frac{5 x}{3}=\frac{5}{7}\left(\frac{72-5 x}{3}\right) \Leftrightarrow 7 x=72-5 x \\
& \Leftrightarrow 12 x=72 \Leftrightarrow x=6 .
\end{aligned}
\)
Hence, speed \(=6 \mathrm{~km} / \mathrm{hr}=\left(6 \times \frac{5}{18}\right) \mathrm{m} / \mathrm{sec}=\frac{5}{3} \mathrm{~m} / \mathrm{sec}=1 \frac{2}{3} \mathrm{~m} / \mathrm{sec}\)
A trip to a destination is made in the following way:900 km by train at an average speed of \(60 \mathrm{~km} / \mathrm{hr}\), \(3000 \mathrm{~km}\) by plane at an average speed of \(500 \mathrm{~km} / \mathrm{hr}, 400 \mathrm{~km}\) by boat at an average speed of \(25 \mathrm{~km} / \mathrm{hr}, 15\) \(\mathrm{km}\) by taxi at an average speed of \(45 \mathrm{~km} / \mathrm{hr}\). What is the average speed for the entire journey? (I.A.S., 2008)
Total distance travelled \(=(900+3000+400+15) \mathrm{km}=4315 \mathrm{~km}\).
\(
\begin{aligned}
\text { Total time taken } & =\left(\frac{900}{60}+\frac{3000}{500}+\frac{400}{25}+\frac{15}{45}\right) \mathrm{hr} \\
& =\left(15+6+16+\frac{1}{3}\right) \mathrm{hr}=37 \frac{1}{3} \mathrm{hr}=\frac{112}{3} \mathrm{hr} .
\end{aligned}
\)
\(\therefore \quad\) Average speed for the whole journey
\(
=\left(4315 \times \frac{3}{112}\right) \mathrm{km} / \mathrm{hr}=115 \frac{65}{112} \mathrm{~km} / \mathrm{hr}
\)
Peter can cover a certain distance in 1 hr. 24 min. by covering two-third of the distance at 4 kmph and the rest at 5 kmph. Find the total distance.
\(
\frac{\frac{2}{3} x}{4}+\frac{\frac{1}{3} x}{5}=\frac{7}{5} \Leftrightarrow \frac{x}{6}+\frac{x}{15}=\frac{7}{5} \Leftrightarrow 7 x=42 \Leftrightarrow x=6 .
\)
Total distance \(=6 \mathrm{~km}\).
One-third of a certain journey was covered at the speed of \(20 \mathrm{~km} / \mathrm{hr}\), one-fourth at \(30 \mathrm{~km} / \mathrm{hr}\) and the rest at the speed of \(50 \mathrm{~km} / \mathrm{hr}\). Find the average speed per hour for the whole journey. (A.A.O. Exam., 2009)
Let the total distance be \(x \mathrm{~km}\). Then,
Distance covered at \(20 \mathrm{~km} / \mathrm{hr}=\frac{x}{3} \mathrm{~km} ;\) Distance covered at \(30 \mathrm{~km} / \mathrm{hr}=\frac{x}{4} \mathrm{~km}\);
Distance covered at \(50 \mathrm{~km} / \mathrm{hr}=\left[x-\left(\frac{x}{3}+\frac{x}{4}\right)\right] \mathrm{km}=\frac{5 x}{12} \mathrm{~km}\)
Total time taken \(=\left[\frac{(x / 3)}{20}+\frac{(x / 4)}{30}+\frac{(5 x / 12)}{50}\right]\) hrs
\(
=\left(\frac{x}{60}+\frac{x}{120}+\frac{x}{120}\right) \mathrm{hrs}=\frac{4 x}{120} \mathrm{hrs}=\frac{x}{30} \mathrm{hrs} \text {. }
\)
\(\therefore \quad\) Average speed for the whole journey \(=\left(x \times \frac{30}{x}\right) \mathrm{km} / \mathrm{hr}=30 \mathrm{~km} / \mathrm{hr}\).
A man travelled from the village to the post-office at the rate of \(25 \mathrm{kmph}\) and walked back at the rate of \(4 \mathrm{kmph}\). If the whole journey took 5 hours 48 minutes, find the distance of the post-office from the village.
Average speed \(=\left(\frac{2 x y}{x+y}\right) \mathrm{km} / \mathrm{hr}=\left(\frac{2 \times 25 \times 4}{25+4}\right) \mathrm{km} / \mathrm{hr}=\frac{200}{29} \mathrm{~km} / \mathrm{hr}\).
Distance travelled in 5 hours 48 minutes, i.e., \(5 \frac{4}{5} \mathrm{hrs}=\left(\frac{200}{29} \times \frac{29}{5}\right) \mathrm{km}=40 \mathrm{~km}\).
\(\therefore \quad\) Distance of the post-office from the village \(=\left(\frac{40}{2}\right)=20 \mathrm{~km}\).
An aeroplane flies along the four sides of a square at the speeds of \(100,200,300\) and \(400 \mathrm{~km} / \mathrm{hr}\). Find the average speed of the plane around the field. (P.C.S., 2009)
Let each side of the square be \(x \mathrm{~km}\) and let the average speed of the plane around the field be \(y \mathrm{~km} / \mathrm{hr}\). Then, \(\frac{x}{100}+\frac{x}{200}+\frac{x}{300}+\frac{x}{400}=\frac{4 x}{y} \Leftrightarrow \frac{25 x}{1200}=\frac{4 x}{y} \Leftrightarrow y=\left(\frac{1200 \times 4}{25}\right)=192\).
\(\therefore \quad\) Average speed \(=192 \mathrm{~km} / \mathrm{hr}\)
A fast train takes 3 hours less than a slow train for a journey of \(600 \mathrm{~km}\). If the speed of the slow train is \(10 \mathrm{~km} / \mathrm{hr}\) less than that of the fast train, then find the speeds of the two trains. (M.A.T., 2006)
Let the speed of the fast train be \(x \mathrm{~km} / \mathrm{hr}\).
The, speed of the slow train \(=(x-10) \mathrm{km} / \mathrm{hr}\).
\(
\begin{aligned}
\therefore \quad & \frac{600}{(x-10)}-\frac{600}{x}=3 \Leftrightarrow 600 x-600(x-10)=3 x(x-10) \\
& \Leftrightarrow x^2-10 x-2000=0 \Leftrightarrow x^2-50 x+40 x-2000=0 \\
& \Leftrightarrow x(x-50)+40(x-50)=0 \Leftrightarrow(x-50)(x+40)=0 \Leftrightarrow x=50 .
\end{aligned}
\)
Hence, speed of fast train \(=50 \mathrm{~km} / \mathrm{hr}\) and speed of slow train \(=40 \mathrm{~km} / \mathrm{hr}\).
By walking at \(\frac{3}{4}\) of his usual speed, a man reaches his office 20 minutes later than his usual time. Find the usual time taken by him to reach his office. (S.S.C., 2010)
New speed \(=\frac{3}{4}\) of usual speed.
\(\therefore \quad\) New time taken \(=\frac{4}{3}\) of usual time.
So, \(\left(\frac{4}{3}\right.\) of the usual time \()-\) (usual time) \(=20 \mathrm{~min}\)
\(\Rightarrow \quad \frac{1}{3}\) of the usual time \(=20 \mathrm{~min} \Rightarrow\) Usual time \(=60 \mathrm{~min}=1 \mathrm{hr}\).
A person reaches his destination 40 minutes late if his speed is \(3 \mathrm{~km} / \mathrm{hr}\), and reaches 30 minutes before time if his speed is \(4 \mathrm{~km} / \mathrm{hr}\). Find the distance of his destination from his starting point. (S.S.C., 2007)
Let the required distance be \(x \mathrm{~km}\).
Difference in the times taken at two speeds \(=70 \mathrm{~min}=\frac{7}{6} \mathrm{hr}\).
\(
\therefore \quad \frac{x}{3}-\frac{x}{4}=\frac{7}{6} \Leftrightarrow 4 x-3 x=14 \Leftrightarrow x=14 \text {. }
\)
Hence, the required distance is \(14 \mathrm{~km}\).
A carriage driving in a fog passed a man who was walking at the rate of 3 kmph in the same direction. He could see the carriage for 4 minutes and it was visible to him upto a distance of 100 m. What was the speed of the carriage?
Let the speed of the carriage be \(x \mathrm{kmph}\). Then, relative speed \(=(x-3) \mathrm{kmph}\).
Distance covered in \(4 \mathrm{~min}\) i.e., \(\frac{1}{15} \mathrm{hr}\) at relative speed \(=100 \mathrm{~m}=\frac{1}{10} \mathrm{~km}\).
\(
\therefore \quad(x-3)=\frac{1}{10} \times 15=\frac{3}{2} \Leftrightarrow x=3+\frac{3}{2}=\frac{9}{2}=4 \frac{1}{2} \text {. }
\)
Hence, speed of the carriage \(=4 \frac{1}{2} \mathrm{kmph}\).
A train after travelling \(150 \mathrm{~km}\) meets with an accident and then proceeds at \(\frac{3}{5}\) of its former speed and arrives at its destination 8 hours late. Had the accident occurred \(360 \mathrm{~km}\) further, it would have reached the destination 4 hours late. What is the total distance travelled by the train? (M.A.T., 2007)
Let the original speed of the train be \(x \mathrm{~km} / \mathrm{hr}\).
Then, \(\frac{360}{\left(\frac{3}{5} x\right)}-\frac{360}{x}=4 \Leftrightarrow \frac{600}{x}-\frac{360}{x}=4 \Leftrightarrow \frac{240}{x}=4 \Leftrightarrow x=60\).
Let the total distance travelled by the train be \(y \mathrm{~km}\).
Then, \(\left[\frac{150}{60}+\frac{(y-150)}{\left(\frac{3}{5} \times 60\right)}\right]-\frac{y}{60}=8 \Leftrightarrow \frac{5}{2}+\frac{(y-150)}{36}-\frac{y}{60}=8 \Leftrightarrow 2 x=1740 \Leftrightarrow x=870\).
Hence, required distance \(=870 \mathrm{~km}\).
A ship \(77 \mathrm{~km}\) from the shore, springs a leak which admits \(2 \frac{1}{4}\) tonnes of water in \(5 \frac{1}{2}\) minutes. 92 tonnes of water would sink it. But the pumps can throw out 12 tonnes of water per hour. Find the average rate of sailing so that the ship may just reach the shore as it begins to sink.
Quantity of water let in by the leak in \(1 \mathrm{~min}\)
\(
=\frac{\left(2 \frac{1}{4}\right)}{\left(5 \frac{1}{2}\right)} \text { tonnes }=\left(\frac{9}{4} \times \frac{2}{11}\right) \text { tonnes }=\frac{9}{22} \text { tonnes. }
\)
Quantity of water thrown out by the pumps in \(1 \mathrm{~min}=\left(\frac{12}{60}\right)\) tonnes \(=\frac{1}{5}\) tonnes.
Net quantity of water filled in the ship in \(1 \mathrm{~min}=\left(\frac{9}{22}-\frac{1}{5}\right)\) tonnes \(=\frac{23}{110}\) tonnes.
\(\frac{23}{110}\) tonnes water is filled in \(1 \mathrm{~min}\).
92 tonnes water is filled in \(\left(\frac{110}{23} \times 92\right) \mathrm{min}=440 \mathrm{~min}=\frac{22}{3} \mathrm{hrs}\).
\(
\text { Hence, required speed }=\frac{77}{(22 / 3)} \mathrm{km} / \mathrm{hr}=\left(77 \times \frac{3}{22}\right) \mathrm{km} / \mathrm{hr}=10.5 \mathrm{~km} / \mathrm{hr} \text {. }
\)
Excluding the stoppages, the speed of a bus is \(64 \mathrm{~km} / \mathrm{hr}\) and including the stoppages, the speed of the bus is \(48 \mathrm{~km} / \mathrm{hr}\). For how many minutes does the bus stop per hour? (Bank P.O., 2009)
Due to stoppage, the bus covers \((64-48)=16 \mathrm{~km}\) less per hour.
Time taken to cover \(16 \mathrm{~km}=\left(\frac{16}{64} \times 60\right) \mathrm{min}=15 \mathrm{~min}\).
Hence, stoppage time per hour \(=15 \mathrm{~min}\).
An aeroplane started 30 minutes later than the scheduled time from a place \(1500 \mathrm{~km}\) away from its destination. To reach the destination at the scheduled time the pilot had to increase the speed by \(250 \mathrm{~km} / \mathrm{hr}\). What was the speed of the aeroplane per hour during the journey? (P.C.S., 2006)
Let the original speed of the aeroplane be \(x \mathrm{~km} / \mathrm{hr}\).
\(
\begin{aligned}
& \therefore \quad \frac{1500}{x}-\frac{1500}{(x+250)}=\frac{1}{2} \Leftrightarrow 3000(x+250)-3000 x=x(x+250) \\
& \Leftrightarrow x^2+250 x-750000=0 \\
& \Leftrightarrow x^2+1000 x-750 x-750000=0 \\
& \Leftrightarrow x(x+1000)-750(x+1000)=0 \\
& \Leftrightarrow(x+1000)(x-750)=0 \Leftrightarrow x=750 .
\end{aligned}
\)
Hence, speed of the aeroplane during the journey \(=(750+250) \mathrm{km} / \mathrm{hr}=1000 \mathrm{~km} / \mathrm{hr}\).
Two boys \(A\) and \(B\) start at the same time to ride from Delhi to Meerut, \(60 \mathrm{~km}\) away. A travels \(4 \mathrm{~km}\) an hour slower than B. B reaches Meerut and at once turns back meeting A 12, km from Meerut. Find A’s speed. (M.B.A., 2011)
Let \(A^{\prime}\) s speed \(=x \mathrm{~km} / \mathrm{hr}\). Then, \(B^{\prime}\) s speed \(=(x+4) \mathrm{km} / \mathrm{hr}\).
Clearly, time taken by \(B\) to cover \((60+12)\), i.e., \(72 \mathrm{~km}=\) time taken by \(A\) to cover \((60-12)\) i.e., \(48 \mathrm{~km}\) \(\therefore \quad \frac{72}{x+4}=\frac{48}{x} \Leftrightarrow 72 x=48 x+192 \Leftrightarrow 24 x=192 \Leftrightarrow x=8\).
Hence, \(A^{\prime}\) s speed \(=8 \mathrm{~km} / \mathrm{hr}\).
A man covers a certain distance on a toy train. Had the train moved \(4 \mathrm{~km} / \mathrm{hr}\) faster, it would have taken 30 minutes less. If it moved \(2 \mathrm{~km} / \mathrm{hr}\) slower, it would have taken 20 minutes more. Find the distance. (M.A.T., 2010)
Let the distance be \(x \mathrm{~km}\) and initial speed be \(y \mathrm{~km} / \mathrm{hr}\).
Then, \(\frac{x}{y}-\frac{x}{y+4}=\frac{30}{60}=\frac{1}{2} \Leftrightarrow \frac{4 x}{y(y+4)}=2 \Leftrightarrow 8 x=y^2+4 y \Leftrightarrow x=\frac{y^2+4 y}{8} \dots(i)\)
And, \(\frac{x}{y-2}-\frac{x}{y}=\frac{20}{60}=\frac{1}{3} \Leftrightarrow \frac{2 x}{y(y-2)}=\frac{1}{3} \Leftrightarrow 6 x=y^2-2 y \Leftrightarrow x=\frac{y^2-2 y}{6} \dots(ii)\)
From \((i)\) and \((i i)\), we have :
\(
\frac{y^2+4 y}{8}=\frac{y^2-2 y}{6} \Leftrightarrow 6 y^2+24 y=8 y^2-16 y \Leftrightarrow 2 y^2=40 y \Leftrightarrow 2 y=40 \Leftrightarrow y=20
\)
Putting \(y=20\) in \((i)\), we get : \(x=60\).
Hence, required distance \(=60 \mathrm{~km}\).
A and B are two stations 390 km apart. A train starts from A at 10 a.m. and travels towards B at 65 kmph. Another train starts from B at 11 a.m. and travels towards A at 35 kmph. At what time do they meet? (M.B.A., 2007)
Suppose they meet \(x\) hours after 10 a.m. Then,
(Distance moved by first in \(x\) hrs) + [Distance moved by second in \((x-1)\) hrs \(]=390\)
\(
\therefore 65 x+35(x-1)=390 \Rightarrow 100 x=425 \Rightarrow x=4 \frac{1}{4} .
\)
So, they meet 4 hrs. \(15 \mathrm{~min}\). after 10 a.m., i.e., at 2.15 p.m.
A goods train leaves a station at a certain time and at a fixed speed. After 6 hours, an express train leaves the same station and moves in the same direction at a uniform speed of 90 kmph. This train catches up the goods train in 4 hours. Find the speed of the goods train.
Let the speed of the goods train be \(x \mathrm{kmph}\).
Distance covered by goods train in 10 hours = Distance covered by express train in 4 hours \(\therefore \quad 10 x=4 \times 90\) or \(x=36\).
So, speed of goods train \(=36 \mathrm{kmph}\).
A thief is spotted by a policeman from a distance of 100 metres. When the policeman starts the chase, the thief also starts running. If the speed of the thief be 8 km / hr and that of the policeman 10 km / hr, how far the thief will have run before he is overtaken?
Relative speed of the policeman \(=(10-8) \mathrm{km} / \mathrm{hr}=2 \mathrm{~km} / \mathrm{hr}\).
Time taken by policeman to cover \(100 \mathrm{~m}=\left(\frac{100}{1000} \times \frac{1}{2}\right) \mathrm{hr}=\frac{1}{20} \mathrm{hr}\).
In \(\frac{1}{20} \mathrm{hrs}\), the thief covers a distance of \(\left(8 \times \frac{1}{20}\right) \mathrm{km}=\frac{2}{5} \mathrm{~km}=400 \mathrm{~m}\).
Two places A and B are 80 km apart from each other on a highway. A car starts from A and another from B at the same time. If they move in the same direction they meet each other in 8 hours. If they move in opposite directions towards each other, they meet in 1 hour 20 minutes. Determine the speeds of the cars. (S.S.C., 2006)
Let their speeds be \(x \mathrm{kmph}\) and \(y \mathrm{kmph}\) respectively.
Then, \(\frac{80}{x-y}=8 \Rightarrow x-y=10 \dots(i)\)
And, \(\frac{80}{x+y}=1 \frac{1}{3}=\frac{4}{3} \Rightarrow x+y=60 \dots(ii)\)
Adding (i) and (ii), we get : \(2 x=70\) or \(x=35\).
Putting \(x=35\) in \((i)\), we get : \(y=25\).
Hence, the speeds of the two cars are \(35 \mathrm{kmph}\) and \(25 \mathrm{kmph}\).
A man takes 6 hours 30 min in going by a cycle and coming back by scooter. He would have lost 2 hours and 10 min by going on cycle both ways. How long would it take him to go by scooter both ways? (M.A.T. 2006)
Let the distance be \(x \mathrm{~km}\). Then,
(Time taken to cover \(x \mathrm{~km}\) by cycle) + (Time taken to cover \(x \mathrm{~km}\) by scooter) \(=6 \mathrm{hr} 30\) min
\(\Rightarrow\) (Time taken to cover \(2 x \mathrm{~km}\) by cycle) + (Time taken to cover \(2 x \mathrm{~km}\) by scooter) \(=13 \mathrm{hrs}\)
But, time taken to cover \(2 x \mathrm{~km}\) by cycle \(=8 \mathrm{hr} 40\) min.
\(\therefore\) Time taken to cover \(2 x \mathrm{~km}\) by scooter \(=13 \mathrm{hrs}-8 \mathrm{hr} 40 \mathrm{~min}=4 \mathrm{hr} 20 \mathrm{~min}\).
Hence, required time \(=4\) hr \(20 \mathrm{~min}\)
Sneha is picked up by her father by car from college every day. The college gets over at 4 p.m. daily. One day, the college got over an hour earlier than usual. Sneha started walking towards her house. Her father, unaware of this fact, leaves his house as usual, meets his daughter on the way, picks her up and they reach the house 15 minutes earlier than usual. What is the ratio of the father’s driving speed to Sneha’s walking speed?
Since 15 minutes are saved, it means that Sneha’s father drives from the meeting point to the college and back to the meeting point in \(15 \mathrm{~min}\). i.e. he can drive from the meeting point to the college in \(\left(\frac{15}{2}\right)=7.5 \mathrm{~min}\).
But he reaches the college daily at 4 p.m. So Sneha and her father meet on the way at \(3: 52 \frac{1}{2} \mathrm{p} . \mathrm{m}\). Thus, Sneha walked for \(52.5 \mathrm{~min}\) and covered the same distance as covered by her father in \(7.5 \mathrm{~min}\). Since speed varies inversely as time taken to cover a distance, we have:
\(\frac{\text { Father’s driving speed }}{\text { Sneha’s walking speed }}=\frac{52.5}{7.5}=\frac{7}{1}\).
Hence, the required ratio \(=7: 1\).
\(
\text { A speed of } 30.6 \mathrm{~km} / \mathrm{hr} \text { is the same as (R.R.B., 2008) }
\)
\(
30.6 \mathrm{~km} / \mathrm{hr}=\left(30.6 \times \frac{5}{18}\right) \mathrm{m} / \mathrm{sec}=\frac{153}{18} \mathrm{~m} / \mathrm{sec}=8.5 \mathrm{~m} / \mathrm{sec}
\)
A man riding his bicycle covers 150 metres in 25 seconds. What is his speed in km per hour? (S.S.C., 2005)
\(
\begin{aligned}
\text { Speed } & =\left(\frac{150}{25}\right) \mathrm{m} / \mathrm{sec}=6 \mathrm{~m} / \mathrm{sec} \\
& =\left(6 \times \frac{18}{5}\right) \mathrm{km} / \mathrm{hr}=\left(\frac{108}{5}\right) \mathrm{km} / \mathrm{hr}=21.6 \mathrm{~km} / \mathrm{hr}
\end{aligned}
\)
A bus covers a distance of \(2924 \mathrm{~km}\) in 43 hours. What is the speed of the bus? (Bank Recruitment, 2008)
\(
\text { Speed }=\left(\frac{2924}{43}\right) \mathrm{km} / \mathrm{hr}=68 \mathrm{~km} / \mathrm{hr}
\)
A is travelling at 72 km per hour on a highway while B is travelling at a speed of 25 metres per second. What is the difference in their speeds in metres per second? (Campus Recruitment, 2010)
\(
\begin{aligned}
& A^{\prime} \text { s speed }=72 \mathrm{~km} / \mathrm{hr}=\left(72 \times \frac{5}{18}\right) \mathrm{m} / \mathrm{sec}=20 \mathrm{~m} / \mathrm{sec} \\
& B^{\prime} \text { s speed }=25 \mathrm{~m} / \mathrm{sec} \\
& \text { Difference }=(25-20) \mathrm{m} / \mathrm{sec}=5 \mathrm{~m} / \mathrm{sec}
\end{aligned}
\)
motorist travelled between two towns, which are \(65 \mathrm{~km}\) apart, in 2 hours and 10 minutes. Find the speed in metres per minute. (R.R.B., 2006)
Distance covered \(=65 \mathrm{~km}=65000 \mathrm{~m}\).
Time taken \(=2 \mathrm{hrs} 10 \mathrm{~min}\)
\(=[(2 \times 60)+10] \mathrm{min}=130 \mathrm{~min}\).
\(\therefore\) Speed \(=\left(\frac{65000}{130}\right) \mathrm{m} / \mathrm{min}=500 \mathrm{~m} / \mathrm{min}\).
In track meets both 100 yards and 100 metres are used as distances. By how many metres is 100 metres longer than 100 yards?
\(
\begin{aligned}
& 1 \text { yard }=0.9144 \mathrm{~m} \Rightarrow 100 \text { yards }=(100 \times 0.9144) \mathrm{m}=91.44 \mathrm{~m} \\
& \therefore \text { Required difference }=(100-91.44) \mathrm{m}=8.56 \mathrm{~m} .
\end{aligned}
\)
A man covered a distance of \(180 \mathrm{~km}\) in 4 hours on a bike. How much distance will be cover on a bicycle in 8 hours if he rides the bicycle at one-sixth the speed of the bike? (Bank Recruitment, 2010)
Speed of the bike \(=\left(\frac{180}{4}\right) \mathrm{km} / \mathrm{hr}=45 \mathrm{~km} / \mathrm{hr}\)
Speed of the bicycle \(=\left(\frac{1}{6} \times 45\right) \mathrm{km} / \mathrm{hr}=7.5 \mathrm{~km} / \mathrm{hr}\).
\(\therefore\) Required distance \(=(7.5 \times 8) \mathrm{km}=60 \mathrm{~km}\).
The ratio of the speeds of a car, a train and \(a\) bus is \(5: 9: 4\). The average speed of the car, the bus and the train is \(72 \mathrm{~km} / \mathrm{hr}\). What is the average speed of the car and the train together? (Bank P.O., 2010)
Let the speeds of the car, train and bus be \(5 x, 9 x\) and \(4 x\) \(\mathrm{km} / \mathrm{hr}\) respectively.
Then, \(\frac{5 x+9 x+4 x}{3}=72 \Leftrightarrow 6 x=72 \Leftrightarrow x=12\).
\(\therefore\) Speed of the car \(=60 \mathrm{~km} / \mathrm{hr}\);
speed of the train \(=108 \mathrm{~km} / \mathrm{hr}\).
Average speed of car and train
\(
=\left(\frac{60+108}{2}\right) \mathrm{km} / \mathrm{hr}=84 \mathrm{~km} / \mathrm{hr} .
\)
Car A travels at the speed of \(65 \mathrm{~km} / \mathrm{hr}\) and reaches its destination in 8 hours. Car B travels at the speed of \(70 \mathrm{~km} / \mathrm{hr}\) and reaches its destination in 4 hours. What is the ratio of the distance covered by car A and car B respectively? (Bank P.O., 2010)
\(
\text { Required ratio }=(65 \times 8):(70 \times 4)=520: 280=13: 7 .
\)
The average speed of a bus is one-third of the speed of a train. The train covers \(1125 \mathrm{~km}\) in 15 hours. How much distance will the bus cover in 36 minutes? (Bank Recruitment, 2010)
None of theseSpeed of the train \(=\left(\frac{1125}{15}\right) \mathrm{km} / \mathrm{hr}=75 \mathrm{~km} / \mathrm{hr}\).
Speed of the bus \(=\left(\frac{1}{3} \times 75\right) \mathrm{km} / \mathrm{hr}=25 \mathrm{~km} / \mathrm{hr}\).
Distance covered by the bus in \(60 \mathrm{~min}=25 \mathrm{~km}\).
Distance covered by the bus in \(36 \mathrm{~min}\)
\(
=\left(\frac{25}{60} \times 36\right) \mathrm{km}=15 \mathrm{~km}
\)
The mileage of a motorbike \(A\) and a motorbike \(B\) is \(42 \mathrm{~km}\) per litre and \(52 \mathrm{~km}\) per litre respectively. Motorbike \(A\) covered \(294 \mathrm{~km}\) and motorbike \(B\) covered \(208 \mathrm{~km}\). If the cost of 1 litre of petrol is \(₹ 48\), how much amount would be spent on petrol to cover the total distance by both the motor bikes together? (Bank P.O., 2010)
Quantity of petrol consumed by both the motorbikes
\(
\begin{aligned}
& =\left(\frac{294}{42}+\frac{208}{52}\right) \text { litres }=11 \text { litres. } \\
& \therefore \text { Total amount spent on petrol }=\text { Rs }(48 \times 11)=₹ 528 .
\end{aligned}
\)
A train leaves Delhi at 4.10 P.M. and reaches Aligarh at 7.25 P.M. The average speed of the train is 40 \(\mathrm{km} / \mathrm{hr}\). What is the distance from Delhi to Aligarh? (R.R.B., 2006)
Time taken \(=3 \mathrm{hrs} 15 \mathrm{~min}=3 \frac{1}{4} \mathrm{hrs}=\frac{13}{4} \mathrm{hrs}\).
\(
\therefore \text { Required distance }=\left(40 \times \frac{13}{4}\right) \mathrm{km}=130 \mathrm{~km}
\)
\(A\) is 10 miles west of \(B\). C is 30 miles north of \(B. D\) is 20 miles east of \(C\). What is the distance from \(A\) to \(D\)? (M.B.A., 2006)
Required distance
\(
\begin{aligned}
& =A D \quad \sqrt{(A E)^2+(D E)^2} \\
& =\sqrt{(30)^2+(30)^2} \\
& =\sqrt{900+900}=\sqrt{1800} \\
& =30 \sqrt{2} \text { miles. }
\end{aligned}
\)
A plane flying north at \(500 \mathrm{mph}\) passes over a city at 12 noon. A plane flying east at the same altitude passes over the same city at \(12: 30 \mathrm{P} M\). The plane is flying east at \(400 \mathrm{mph}\). To the nearest hundred miles, how far apart are the two planes at 2 P.M.?
Distance covered by the first plane till 2 P.M., i.e., in 2 hrs \(=(500 \times 2)\) miles \(=1000\) miles.
Distance covered by the second plane till 2 P.M., i.e., in
\(
\begin{aligned}
& 1 \frac{1}{2} \text { hrs }=\left(400 \times \frac{3}{2}\right) \text { miles }=600 \text { miles. } \\
& \therefore \text { Required distance } \\
& \qquad=A B=\sqrt{(1000)^2+(600)^2} \\
& \quad=\sqrt{1000000+360000}
\end{aligned}
\)
\(
\begin{aligned}
& =\sqrt{1360000} \text { miles }=200 \sqrt{34} \text { miles } \\
& =1166 \text { miles } \approx 1200 \text { miles. }
\end{aligned}
\)
A train travels at the speed of \(65 \mathrm{~km} / \mathrm{hr}\) and halts at 8 junctions for a certain time. It covers a distance of \(1300 \mathrm{~km}\) in 1 day (24 hours). How long does the train stop at each junction, if it halts for the same period of time at all the junctions? (Bank P.O., 2006)
Time taken to cover \(1300 \mathrm{~km}=\left(\frac{1300}{65}\right) \mathrm{hrs}=20 \mathrm{hrs}\). Halt time \(=(24-20) \mathrm{hrs}=4 \mathrm{hrs}\).
Halting time at each junction \(=\left(\frac{4 \times 60}{8}\right) \mathrm{min}=30 \mathrm{~min}\).
Jane travelled \(\frac{4}{7}\) as many miles on foot as by water and \(\frac{2}{5}\) as many miles on horseback as by water. If she covered a total of 3036 miles, how many miles did she travel on foot? (SNAP, 2005)
Suppose Jane travelled \(x\) miles by water, \(\left(\frac{4 x}{7}\right)\) miles on foot and \(\left(\frac{2 x}{5}\right)\) miles on horseback.
Then, \(x+\frac{4 x}{7}+\frac{2 x}{5}=3036 \Leftrightarrow \frac{69 x}{35}=3036\)
\(
\Leftrightarrow x=\left(\frac{3036 \times 35}{69}\right)=1540 .
\)
\(\therefore\) Distance travelled on foot \(=\left(\frac{4}{7} \times 1540\right)\) miles \(=880\) miles.
A star is \(8.1 \times 10^{13} \mathrm{~km}\) away from the earth. Suppose light travels at the speed of \(3.0 \times 10^5 \mathrm{~km}\) per second. How long will it take the light from the star to reach the earth? (R.R.B., 2005)
\(
\begin{aligned}
\text { Required time } & =\left(\frac{8.1 \times 10^{13}}{3.0 \times 10^5}\right) \text { seconds }=2.7 \times 10^8 \mathrm{sec} \\
& =\left(\frac{2.7 \times 10^8}{60 \times 60}\right) \mathrm{hrs}=7.5 \times 10^4 \mathrm{hrs} .
\end{aligned}
\)
Akash leaves home for school which is \(12 \mathrm{~km}\) from his house. After the school, he goes to his club which is \(7 \mathrm{~km}\) from his school. If his house, school and club all fall in a line, then what is the minimum distance he has to travel to get back home?
For the distance to be minimum, the club must lie between Akash’s home and school.
Hence, required distance \(=(12-7) \mathrm{km}=5 \mathrm{~km}\).
A train covers a distance of \(193 \frac{1}{3} \mathrm{~km}\) in \(4 \frac{1}{4}\) hours with one stoppage of 10 minutes, two of 5 minutes and one of 3 minutes on the way. The average speed of the train is
Actual time taken for the journey
\(
\begin{aligned}
& =4 \text { hrs } 15 \mathrm{~min}-(10+2 \times 5+3) \mathrm{min} \\
& =4 \mathrm{hrs} 15 \mathrm{~min}-23 \mathrm{~min}=3 \mathrm{hrs} 52 \mathrm{~min}=3 \frac{26}{30} \mathrm{hrs}=\frac{116}{30} \mathrm{hrs} . \\
& \therefore \text { Average speed }=\left(\frac{580}{3} \times \frac{30}{116}\right) \mathrm{km} / \mathrm{hr}=50 \mathrm{~km} / \mathrm{hr} .
\end{aligned}
\)
Deepa rides her bike at an average speed of 30 \(\mathrm{km} / \mathrm{hr}\) and reaches her destination in 6 hours. Hema covers the same distance in 4 hours. If Deepa increases her average speed by \(10 \mathrm{~km}\) / \(\mathrm{hr}\) and Hema increases her average speed by \(5 \mathrm{~km} / \mathrm{hr}\), what would be the difference in their time taken to reach the destination?
Deepa’s original speed \(=30 \mathrm{~km} / \mathrm{hr}\).
Deepa’s new speed \(=(30+10) \mathrm{km} / \mathrm{hr}=40 \mathrm{~km} / \mathrm{hr}\).
Distance \(=(30 \times 6) \mathrm{km}=180 \mathrm{~km}\).
Hema’s original speed \(=\left(\frac{180}{4}\right) \mathrm{km} / \mathrm{hr}=45 \mathrm{~km} / \mathrm{hr}\).
Hema’s new speed \(=(45+5) \mathrm{km} / \mathrm{hr}=50 \mathrm{~km} / \mathrm{hr}\).
Difference in time
\(
=\left(\frac{180}{40}-\frac{180}{50}\right) \mathrm{hrs}=\frac{9}{10} \mathrm{hrs}=\left(\frac{9}{10} \times 60\right) \mathrm{min}=54 \mathrm{~min} .
\)
A monkey climbing up a pole ascends 6 metres and slips 3 metres in alternate minutes. If the pole is 60 metres high, how long will it take the monkey to reach the top? (Campus Recruitment, 2010)
Net height ascended in \(2 \mathrm{~min}=(6-3) \mathrm{m}=3 \mathrm{~m}\).
Net height ascended in \(36 \mathrm{~min}=\left(\frac{3}{2} \times 36\right) \mathrm{m}=54 \mathrm{~m}\).
In the 37 th \(\mathrm{min}\), the monkey ascends \(6 \mathrm{~m}\) and reaches the top.
Hence, total time taken \(=37\) minutes.
An aeroplane flies twice as fast as a train which covers 60 miles in 80 minutes. What distance will the aeroplane cover in 20 minutes? (E.S.I.C., 2006)
Time taken to cover 60 miles \(=80 \mathrm{~min}=\frac{4}{3} \mathrm{hrs}\).
\(\therefore\) Speed of the train \(=\left(60 \times \frac{3}{4}\right) \mathrm{mph}=45 \mathrm{mph}\).
Speed of the aeroplane \(=(2 \times 45) \mathrm{mph}=90 \mathrm{mph}\).
Distance covered by the aeroplane in \(60 \mathrm{~min}=90\) miles.
Distance covered by the aeroplane in \(20 \mathrm{~min}\)
\(
=\left(\frac{90}{60} \times 20\right) \text { miles }=30 \text { miles. }
\)
A boy is running at a speed of \(p kmph\) to cover a distance of \(1 km\). But, due to the slippery ground, his speed is reduced by \(q kmph (p>q)\). If he takes \(r\) hours to cover the distance, then (M.B.A., 2006)
\(
\text { Speed }=\frac{\text { Distance }}{\text { Time }} \Rightarrow p-q=\frac{1}{r} \text {. }
\)
Ravi can walk a certain distance in 40 days when he rests 9 hours a day. How long will he take to walk twice the distance, twice as fast and rest twice as long each day? (A.A.O. Exam, 2010)
100 daysLet the required number of days be \(x\).
More distance, More days required (Direct Proportion)
More speed, Less days required (Indirect Proportion)
More resting hours, More days required (Direct Proportion)
\(\left.\begin{array}{ll}\text { Distance } & 1: 2 \\ \text { Speed } & 2: 1 \\ \text { Resting hours } & 9: 18\end{array}\right\}:: 40: x\)
\(
\begin{aligned}
& \therefore \quad 1 \times 2 \times 9 \times x= \\
& 2 \times 1 \times 18 \times 40 \Leftrightarrow x=\frac{2 \times 18 \times 40}{2 \times 9}=80 .
\end{aligned}
\)
A car is driven at the speed of \(100 \mathrm{~km} / \mathrm{hr}\) and stops for 10 minutes at the end of every \(150 \mathrm{~km}\). To cover a distance of \(1000 \mathrm{~km}\), it will take
Time taken to cover \(150 \mathrm{~km}=(1 \mathrm{hr} 30 \mathrm{~min}+10 \mathrm{~min})\)
\(
=1 \mathrm{hr} 40 \mathrm{~min}=1 \frac{2}{3} \mathrm{hr}=\frac{5}{3} \mathrm{hr} \text {. }
\)
Time taken to cover \((150 \times 6)\) i.e., \(900 \mathrm{~km}\)
\(
=\left(\frac{5}{3} \times 6\right) \text { hrs. }=10 \mathrm{hrs} \text {. }
\)
Remaining \(100 \mathrm{~km}\) is covered in 1 hour.
Total time taken \(=(10+1)\) hrs \(=11\) hrs.
A man takes 50 minutes to cover a certain distance at a speed of \(6 \mathrm{~km} / \mathrm{hr}\). If he walks with a speed of \(10 \mathrm{~km} / \mathrm{hr}\), he covers the same distance in
\(
\begin{aligned}
& \text { Distance }=\text { Speed } \times \text { Time }=\left(6 \times \frac{50}{60}\right) \mathrm{km}=5 \mathrm{~km} . \\
& \therefore \text { Required time }=\frac{\text { Distance }}{\text { Speed }}=\left(\frac{5}{10}\right) \mathrm{hrs}=\frac{1}{2} \mathrm{hr}=30 \mathrm{~min} \text {. }
\end{aligned}
\)
A truck covers a distance of 550 metres in 1 minute whereas a bus covers a distance of \(33 \mathrm{kms}\) in 45 minutes. The ratio of their speeds is
\(
\text { Ratio of speeds }=\left(\frac{550}{60} \times \frac{18}{5}\right):\left(\frac{33}{45} \times 60\right)=33: 44=3: 4 \text {. }
\)
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