Question

A car covers a distance in 40 min with an average speed of 60km/h, what should be the average speed to cover the same distance

Answer 1

since equal distances are covered at 60 kmph and 40 kmph, we can apply the formula 2xy/(x+y)
Average speed= 2×40×6040+602×40×6040+60 = 48 kmph

This formula works as follows

Let the distance to one side = x
Total distance = 2x 

Time taken for the forward journey = x60x60
Time taken for the return journey = x40x40
Total time = x60+x40=100x2400x60+x40=100x2400

Average speed = Total distanceTotal Time=2x(100x2400)Total distanceTotal Time=2x(100x2400) = 48 kmph