Question

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

Answer 1

Answer:

BOY RUN AT A INFORMA MOTION SO BOY SPEED FOR NEXT 20 KM/H IS 9KM/H

Answer 2

Answer:

13 km/h

Explanation:

Given:

• The speed of the boy in first 10 minutes = 9 km/h
• Average speed of the boy = 12 km/h

To find:

• Speed required for the next 20 minutes to get an average speed of 12 km/hr

Average speed=Total distance/Total time

Total time = 10 minutes + 20 minutes = 30 minutes

1 hour = 60 minutes, so 30 minutes = 1/2 hour

Total distance = Distance covered in the first 10 seconds + Distance covered in the next 10 seconds

Distance covered in first 10 seconds = 9×1/6 = 1.5 km

So substituting the above values:

$12 = \dfrac{1.5+d2}{\frac{1}{2} }$

6 = 1.5 + d2

4.5 = d2

Distance = 4.5 km

Time = 20 minutes

Speed = distance/time

Speed = 4.5/1/3

Speed = 13.5 km/h

The speed required is 13 km/h