A man walks on a straight road form his home to a market 2.5 km away with speed of 5 `(km)/(hr)`. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 `(km)/(hr)`. The average speed of the man over the intervel of time 0 to 40 min is equal to

Options

A. 5 km/h
B. `25/4` km/h
C. `30/4` km/h
D. `45/8` km/h

Answer

D

Explanation

Time to reach market `= (2.5km)/(5) = 1/2hr`
Distance travel (return back) = 7.5 xx 10/60`
`1 = 1.25 km`
`v_(avg) = (2.5+1.25)/(40//60) = 45/8 km//hr`