Question

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

Answer 1

For the first part of journey,

Speed=9km/h,Time=10min=10/60 hour=1/6 hour

So distance=Speed x Time

Distance=9x(1/6)=3/2 km

For the second part of journey,

Suppose speed=x km/h

Time taken=20 min=20/60=1/3 hour

Then distance=x/3 km

Now,

Average speed=Total distance travelled / Total time taken