Question

A boy runs for 10 min at a uniform speed of
9 km/h. At what speed should he run for the
next 20 min so that the average speed comes to
12 km/hr?
​

Answer 1

Answer:

13.5 km/h

Explanation:

average speed = total distance/total time

let the required speed = v

(9×10/60 + 20v/60)/30/60 = 12 km/h

(9×10 + 20v) = 12×30 = 360  , 20v = 270 , v = 13.5 km/h

Answer 2

Answer:

Explanation:

9×10/60 + 20v/60)/30/60 = 12 km/h

(9×10 + 20v) = 12×30 = 360 , 20v = 270 , v = 13.5 km/h