Question

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

Answer 1

Answer:

12 km/h

Step-by-step explanation:

12 km/h because he needs to go 1.25 times faster than he was going before.

Answer 2

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Given ->

Average speed = 12km/hr

Total time = (10+20) min

= (30)min

= 1/2 hr

We know

Average speed = Total distance / total time

= (d1+d2)/(t1+t2).......(1)

We have

= d1=s*t

= 9*1/6....{10 min=1/6 hr}

= 3/2 km........ (2)

Let find d2 from eq (1) and (2)

12 = (3/2+d2) /1/2

6 = 3/2+d2

d2 = 9/2 km........ (3)

So, from(3),

Speed = d2/t2

= (9/2)/(1/3)

= 27/2

= 13.5 km/hr

The Run for next 20 min should be at 13.5 km/hr so that the average speed comes to 12 km/hr.