A boy goes to a cycle shop by walk at ` 5 km h^(-1)` and comes back home by cycle at a speed of ` 15 km h^(-1)` , find out the average speed of the boy.

Explanation

Speed = `("distance")/("time")`
Time = ` ("distance")/("time")`
Take the distance as x .
Time taken to reach the cycle shope ` t_(1) =x/5`
Time taken to reture `t_(2) = x/15`
Average speed = `("total distance")/("total time") = (x + x) /(t_(1) +t_(2))`
` = (2x)/(x+5 + x+15) = (2x)/(3x+x/15)`
` (15 xx 2x)/(4x) = 30/4 = 7.5 km h^(-1)`