A bo walks to his school at a distance of 6 km with constant speed of `2.5 kmh^(-1)` and walks back with a constant speed of `4 kmh^(-1)`. His average speed for round trip expressed in `kmh^(-1)`, is

Options

A. `(24)/(13) km h^(-1)`
B. `(40)/(13)kmh^(-1)`
C. `3 km h^(-1)`
D. `4.8km h^(-1)`

Answer

b

Explanation

Time taken by a boy when walking to his school is `t_(1)`
where `t_(1)=(6)/(2.5)` hour.
Again time taken when walking from school to home is `t_(2)`
Average speed `=(12km)/((6)/(2.5)+(6)/(4))=(2xx2.5xx4)/(6.5)m//s`
`=(200)/(65)=(40)/(13)km//h`