Question

A bus travelling the first one-third distance at a speed of 10 km/h, the next one-third at 20 km/h and at last one-third at 60 km/h. The average speed of the bus is

(a) 9 km/h

(b) 16 km/h

(c)  18 km/h

(d) 48 km/h.

Answer 1

Correct option (c)  18 km/h

Explanation:

Total distance travelled = s 

Answer 2

Option (c) 18km/h

Explanation

Let the total distance covered be 3x km.

So time of covering first x km with speed 10km/h will be =x/10h

Time to cover 2nd xkm with speed 20km/h will be = x/20 h

And the time to cover last x km with speed 60km/h will be = x/60 h

Hence average speed

= Total distance covered/ total time required

= 3x/(x/10+x/20+x/60)

=3×60/(6+3+1)

=18 km/ h