Question

john runs for 10 min.at a uinform speed 9km/hr .at what speed should he run for the next 20min. so that the average speed comes 12km/hr ??

Answer 1

avg speed = total distance / total time

12 = ((9/6)+(x/3))/0.5     9/6 is distance in 10 min, x/3 is distance in 20 min and total time is 0.5 hours

Calculate for x  = (6-3/2)*3 = 4.5*3 = 13.5 KM/ hr