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

Average speed (12 km/hr) = Total Distance / Total

Time

D1 + D2 / T1+T2

Total Time = 10 min + 20 min = 30 min = 1/2 Hour

D1 = Speed * Time 9 * 1/6 (10 min = 1/6 hr)

= 3/2km=1.5km

D2 = ?

km 1.5 km

12 = 1.5 + D2/1/2 12 * 1/2 = 1.5 + D2 6 = 1.5 + D2 6 - 1.5 = D2

4.5 km = D2

Speed = Distance / Time = 4.5 / 1/3 (20 min = 1/3 hr)

= 4.5 * 3 (Reciprocal) = 13.5 km/hr

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