Speed, Time and Distance
 A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is

 37.5
 37
 35
 40

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Average speed of whole journey = 2xy kmph x + y = 2 × 50 × 30 kmph 50 + 30 = 2 × 50 × 30 = 37.5 kmph 80 Correct Option: A
Average speed of whole journey = 2xy kmph x + y = 2 × 50 × 30 kmph 50 + 30 = 2 × 50 × 30 = 37.5 kmph 80
 A train runs from Howrah to Bandel at an average speed of 20 km/hr and returns at an average speed of 30 km/hr. The average speed (in km/hr) of the train in the whole journey is

 20
 22.5
 24
 25

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Average speed = 2xy kmph x + y = 2 × 20 × 30 20 + 30 = 2 × 20 × 30 = 24 kmph 50 Correct Option: C
Average speed = 2xy kmph x + y = 2 × 20 × 30 20 + 30 = 2 × 20 × 30 = 24 kmph 50
 A and B are 20 km apart. A can walk at an average speed of 4 km/hour and B at 6 km/hr. If they start walking towards each other at 7 a.m., when they will meet ?

 8.00 a.m.
 8.30 a.m.
 9.00 a.m.
 10.00 a.m.

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If A and B meet after t hours, then
4 t + 6 t = 20
⇒ 10 t = 20⇒ t = 20 = 2 hours. 10
Hence, both will meet at 9 a.m.Correct Option: C
If A and B meet after t hours, then
4 t + 6 t = 20
⇒ 10 t = 20⇒ t = 20 = 2 hours. 10
Hence, both will meet at 9 a.m.
 A train goes from Ballygunge to Sealdah at an average speed of 20 km/hour and comes back at an average speed of 30 km/hour. The average speed of the train for the whole journey is

 27 km/hr
 26 km/hr
 25 km/hr
 24 km/hr

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Required average speed = 2 × 30 × 20 30 + 20
[∵ Distance covered is same]= 2 × 30 × 20 = 24 kmph 50 Correct Option: D
Required average speed = 2 × 30 × 20 30 + 20
[∵ Distance covered is same]= 2 × 30 × 20 = 24 kmph 50
 On a journey across Kolkata, a taxi averages 50 km per hour for 50% of the distance, 40 km per hour for 40% of it and 20 km per hour for the remaining. The average speed (in km/hour) for the whole journey is :

 42
 40
 35
 45

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Total distance = 100 km.
Total time = 50 + 40 + 10 50 40 20 = 1 + 1 + 1 = 5 hours 2 2 ∴ Average speed = 100 × 2 = 40 kmph 5 Correct Option: B
Total distance = 100 km.
Total time = 50 + 40 + 10 50 40 20 = 1 + 1 + 1 = 5 hours 2 2 ∴ Average speed = 100 × 2 = 40 kmph 5