A car travels first half distance between two places with uniform speed of 60 km/hr. What should be its uniform speed (in km/hr) for the second half of the distance so that its average speed over the entire journey becomes 90 km/hr.
A
120
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B
150
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C
180
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D
210
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Solution
The correct option is C180 Let the total distance be 2D
For first half distance D, Time taken=DistanceAverage Speed=D60
For the later half distance D, let the average speed be v
Time taken = Dv
For total journey : Total distance=Average speed×total time 2D=90(D60+Dv)
On Solving , v=180 km/hr