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/hr.

Answer 1

Average speed = total distance / total time,

Distance travelled in 20 min = 18/3 = 6 km,

Let the distance travelled in 40 min be x km ,

(20 min = 1/3 of an hour, 40 min = 2/3 of an hour)

Then : 24 =( x + 6)/(2/3 + 1/3), = x+6/1,

X + 6 = 24km, x = 18km , now let the speed required be y, then we know that y = 18/(2/3)

( speed = distance/time) so y = 18 *3/2 km/hr

 = 27 km/hr

Answer 2

Answer:

 = 27 km/hr

Explanation:

Average speed = total distance / total time,

Distance travelled in 20 min = 18/3 = 6 km,

Let the distance travelled in 40 min be x km ,

(20 min = 1/3 of an hour, 40 min = 2/3 of an hour)

Then : 24 =( x + 6)/(2/3 + 1/3), = x+6/1,

X + 6 = 24km, x = 18km , now let the speed required be y, then we know that y = 18/(2/3)

( speed = distance/time) so y = 18 *3/2 km/hr

 = 27 km/hr

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