Speed, Time and Distance
 A constant distance from Chennai to Bangalore is covered by Express train at 100 km/hr. If it returns to the same distance at 80 km/hr, then the average speed during the whole journey is

 90.20 km/hr
 88.78 km/hr
 88.98 km/hr
 88.89 km/hr

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If same distance are covered at two different speed of x and y kmph, the average speed of journey
= 2xy x + y = 2 × 100 × 80 kmph 100 + 80
= 88.89 kmphCorrect Option: D
If same distance are covered at two different speed of x and y kmph, the average speed of journey
= 2xy x + y = 2 × 100 × 80 kmph 100 + 80
= 88.89 kmph
 A man travels a distance of 24 km at 6 kmph. Another distance of 24 km at 8 kmph and a third distance of 24 km at 12 kmph. His average speed for the whole journey (in kmph) is


8 2 3  8

2 10 13  9


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Total distance
= 24 + 24 + 24 = 72 km.Total time
=24 + 24 + 24 hours 6 8 12
= (4 + 3 + 2) hours = 9 hours∴ Required average speed = Total distance Total time = 72 = 8 kmph. 9 Correct Option: B
Total distance
= 24 + 24 + 24 = 72 km.Total time
=24 + 24 + 24 hours 6 8 12
= (4 + 3 + 2) hours = 9 hours∴ Required average speed = Total distance Total time = 72 = 8 kmph. 9
 A train covers a distance of 3584 km in 2 days 8 hours. If it covers 1440 km on the first day and 1608 km on the second day, by how much does the average speed of the train for the remaining part of the journey differ from that for the entire journey ?

 3 km/hour more
 3 km/hour less
 4 km/hour more
 5 km/hour less

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Remaining distance
= (3584 – 1440 – 1608) km
= 536 km.This distance is covered at the rate of 536 = 67 kmph. 8
Average speed of whole journey= 3584 = 64 kmph 56
∴ Required difference in speed
= (67 – 64) kmph i.e. = 3 kmph
moreCorrect Option: A
Remaining distance
= (3584 – 1440 – 1608) km
= 536 km.This distance is covered at the rate of 536 = 67 kmph. 8
Average speed of whole journey= 3584 = 64 kmph 56
∴ Required difference in speed
= (67 – 64) kmph i.e. = 3 kmph
more
 A man goes from A to B at a uniform speed of 12 kmph and returns with a uniform speed of 4 kmph His average speed (in kmph) for the whole journey is :

 8
 7.5
 6
 4.5

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If two equal distances are covered at two unequal speed of x kmph and y kmph, then average
speed = 2xy kmph x + y = 2 × 12 × 4 = 96 = 6 kmph 12 + 4 16 Correct Option: C
If two equal distances are covered at two unequal speed of x kmph and y kmph, then average
speed = 2xy kmph x + y = 2 × 12 × 4 = 96 = 6 kmph 12 + 4 16
 A man covers half of his journey at 6km/hr and the remaining half at 3km/hr. His average speed is

 9 km/hr
 4.5 km/hr
 4 km/hr
 3 km/hr

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If the same distance are covered at different speed of x kmph and y kmph, the average speed of the
whole journey is given by = 2xy kmph. x + y ∴ Required average speed = 2 × 6 × 3 = 36 = 4 kmph 6 + 3 9 Correct Option: C
If the same distance are covered at different speed of x kmph and y kmph, the average speed of the
whole journey is given by = 2xy kmph. x + y ∴ Required average speed = 2 × 6 × 3 = 36 = 4 kmph 6 + 3 9