Question

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

Answer 1

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Given -

Average speed = 12 km/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 hour}

= 3/2 km (2)

Let's find d2 from (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 minutes should be at 13.5 km/hr so that the average speed comes to 12 km/hr.

Answer 2

Answer:

\huge{\blue{\texttt{\orange A\red N\green S\pink W\blue E\purple R\red࿐}}}ANSWER࿐

Given -

Average speed = 12 km/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 hour}

= 3/2 km (2)

Let's find d2 from (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 minutes should be at 13.5 km/hr so that the average speed comes to 12 km/hr.