A car is moving on a straight road covers one third of the distance with a speed of 20 km/h and the rest with a speed of 60 km/h. The average speed of the car is

Options

A. 40km/hr
B. 80km/hr
C. `46(2)/(3) km//hr`
D. 36 km/hr

Answer

D

Explanation

`t_(1)=((d)/(3))/(20)=(d)/(60)` and `t_(2)=((2d)/(3))/(60)=(d)/(20)`
total time `t=t_(1)+t_(2)`
average speed `=(d)/(t)=(d)/((d)/(60)+(d)/(90))=36 km//hr`.
`=(60xx90)/(150)=36 km//hr`