A bus trvels one third of the distance with a speed of `12 km h^(-1)` and the remaining distance with a speed of `20 km h^(-1)` . The average speed of the bust is __________ `km h^(-1)`

Options

A. 14
B. 20
C. 12
D. 16

Explanation

`t_(1)=(1//3d)/(12)" " t_(1)=(d)/(36)s`
`t_(2)=(2//3d)/(20)" " t_(2)=(d)/(30)s`
total time `t=t_(1)=(d)/(36)+(d)/(30)=d((1)/(36)+(1)/(30))`
`=d((5+6)/(180))=d((11)/(180))s`
`"Average speed"=("Total distance")/("Total time")=(d)/((11d)/(180))`
`=(180)/(11)=16.4 km h^(-1)`