Tuesday, November 15, 2011

A car travels 25km at 25kph, 25km at 50kph and 25km at 75kph UPSC Mains 2011 Question solved

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A car travels 25km at 25kph, 25km at 50kph and 25km at 75kph. Find the average speed of the car for the entire journey.
Consider
Avg. Speed of entire journey = x

Item
Distance
K m
Avg.Speed
Kmph
Time
H
1
25
25
25/25 = 1
2
25
50
25/50=1/2
3
25
75
25/75=1/3
Total
75
x
1+(1/2)+(1/3) = 11/6

Avg. Speed = Total Distance/ Total Time
X = 75/(11/6) = 75 * 6/11 = 40.9 = 41 kmph