Question

A car travels from city A to city B, 120 km apart at an average speed of 50km/h. It then makes a return trip at an average speed of 60km/h. It covers another 120km distance at an average speed of 40km/h. The average speed over the entire 360km will be ______.

Options

• `(50+60+40)/3`km/h

• `(3/(1/50+1/60+1/40))`km/h

• `300/(50+60+40)`km/h

• none of these

Answer 1

A car travels from city A to city B, 120 km apart at an average speed of 50km/h. It then makes a return trip at an average speed of 60km/h. It covers another 120km distance at an average speed of 40km/h. The average speed over the entire 360km will be `underline((3/(1/50+1/60+1/40))"km/h")`.

Explanation:-

`T_1=120/50"hrs",  T_2=120/60" and "T_3=120/40`

`"Total time" = (120/50+120/60+120/40)"hrs"`

Total distance = 3 × 120km

`"Average speed" =(3xx120)/(120/50+120/60+120/40)`

`=(3/(1/50+1/60+1/40))"km/h"`