Question

a boy walks to his school at a distance of 6 km with a constant speed of 2.5 km/h and walks back with a constant speed of 4 km/h . His average speed for round trip expressed in km/h, is
1) 24/13
2) 40/13
3) 3
4) 1/2
correct answer with explanation please​

Answer 1

Answer:

40/13

Explanation:

we have to take out the time taken in both case .

In first case ,

when the boy walks towards the school of distance 6 km so,

so apply the formula of speed

speed =distance /time

speed=2.5km/h

distance=6km

time=?

2.5=6/time

time=6/2.5

=2.4hour

in second case,

when the boy walks towards his home then also the distance will be same of 6 km.

so again apply the formula of speed

speed=distance/time

speed=4km/h

distance=6km

time=?

4=6/time

time=6/4

time=1.5hour

the total distance from home to school and the distance from school to home is 6+6=12km.

the total time is 2.4hour+1.5hour=3.9hour

average speed =total distance/ total time

=12/3.9

=120/39

=40/13