A boy walks to his school at a distance of 6 km with constant speed of 2.5 km/h and walks back with a constant speed of 4 km/h. His average speed for the round trip is:

Options

A. `(24)/(13) kmh^(-1)`
B. `(40)/(13) kmh^(-1)`
C. 3 km/h
D. `1/2Km h^(-1)`

Answer

b

Explanation

`t_1=(6)/(2.5)=(12)/(5)` hr,`t_2=(6)/(4)=(3)/(2)hr`
Total time `(t_1+t_2)=(12)/(5)+(3)/(2)=(39)/(10)hr`.
`v_a=(6+6)/((39)/(10))=(40)/(13) km//hr`