Question

A man walks on a straight road from his
home to a market 2.5 km away with a speed
of 5 km/h. Finding the market closed, he
instantly turns and walks back home with
a speed of 7.5 km/h. The average speed of
the man over the interval of time 0 to
40 min, is equal to
1) 5 km/h
2) 25/4 km/h
km/h
3) 30/4 km/h 4) 45/8 km/h​

Answer 1

Answer:

45/8 km/h

Explanation:

The man walks with a speed 5km/h to cover 2.5km

This means that he covered 2.5km in 2.5/5 hrs = 30 min     ......(i)

Now the man walks with a speed of 7.5km/h to cover 2.5km

This means that he covered 2.5km in 7.5/2.5 hrs = 20 min

This implies that he covered 1.25 km in 10 min     .....(ii)

Adding (i) and (ii)

Time = 30+10 = 40 min = 40/60 hrs

distance = 1.25+2.5 = 3.75km

Therefore the average speed = 3.75/(40/60)

                                                  = 3.75*60/40

                                                  = 45/8 km/h