Ram covers a distance of 100 km with variable speed. During the first half of his journey his speed was 20 km/h and during the rest of his journey his speed was 40 km/h. Calculate the average speed of Ram during the whole course of his motion.

Explanation

`"Distance covered = 100 km"`
`"Time taken by Ram to cover 50 km with speed 20 km/h "(t_(1))=(50)/(20)h=(5)/(2)h`
`"Time taken by Ram to cover next 50 km "(t_(1))=(50)/(40)g=(5)/(4)h`
`"Total time"=t_(1)+t_(2)=(5)/(2)+(5)/(4)=(10+5)/(4)=(15)/(4)h`
`"Average speed"=("Total distance travelled")/("Total time taken to cover that distance")`
`=(100)/(15)xx4=(80)/(3)=26.66km//h`