Question

A boy runs for 20 minutes at a uniform speed of 18km/h .At what speed should he run for the next 40minutes. so that the average speed comes 2okm/hr

Answer 1

average speed is equal to total distance divided by total time
convert 20 minutes into seconds that is 60 into 20 is equal to 1200sec
converting kilometre per hour into metre per second that is multiplied by 5 by 18 this will become 5 metre per second in second case it travels for 40 minutes that is 40 into 60 seconds 2400s

in first case distance travelled is equal to speed into time
that is 1200 multiplied by 5 is equal to 6000meter

let distance travel in second case is equal to Xmeters

according to formula of average speed that is total distance divided by total time


that is 6000 plus x divided by 1200 plus 2400

is equal to 20 into 5 divided by 18 now you can solve this equation easily to find the speed in second case