Question

A boy runs for 20 min at a uniform speed of 18km/h at what speed should he run for the next 40 min.so that the average speed comes 24km/h

Answer 1

Answer:

27 kmph

Explanation:

Distance travelled in first 20 min is

= speed × time

= 18 kmph × 20 min

= 18 kmph × 20 min × [1 hr / (60 min)]

= 18 kmph × (1/3) h

= 6 km

Distance travelled in next 40 min is

= speed × time

= v × 40 min

= v × 40 min × [1 hr / (60 min)]

= 2v/3

Average speed = Total distance / Total time

24 = (6 + 2v/3) / (20 min + 40 min)

24 = (6 + 2v/3)/(60 min)

24 = (6 + 2v/3)/(1 hr)

24 = 6 + 2v/3

18 = 2v/3

v = 18 × 3/2

v = 27 kmph