Question

A man can row at 9km/h in still water. He rows 1.5km upstream and back again. The stream flows at 3km/h. What is his average speed for the whole trip?

Answer 1

8km/h

Explanation:

The computation of the average speed is shown below:

In the case of upstream, the speed is

= 9 - 3

= 6km/h

And, the time would be

= 1.5km ÷ 6

= 0.25h

In the case of downstream, the speed is

= 9 + 3

= 12

The time would be

= 1.5km ÷ 12

= 0.125h

Now the average speed is

= 3 ÷ (0.25 + 0.125)

= 8km/h