Question

27. A bus travels 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 bus is
km h-1.
(a) 14
(b) 20
(c) 12
(d) 16.4

the ans is 16.4
if any one gives its right ans i would rate him
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Answer 1

Let the distance be x.

Therefore,

when speed =12km/h(S1)

then,

distance =1/3x

Remaining distance

=x-1/3x

=2/3x

Speed=20km/h(S2)

T1=(1/3x)/12 = 1/36x

T2=(2/3x)/20=1/30x

Average speed = Total distance/Total time

=x/(1/36x + 1/30x)

=x/(11x/180)

=(x*180)/11x

=180/11(Since x gets cancelled)

=16.33..km/h