Question

A man can row 8 kmph in still water. If in a river running at 2 kmph. it takes him 45 minutes to row to a place and back. how far off is the place?

Answer 1

Speed in still water = 8 kmph

Speed of the river = 2kmph

Find the speed with going upstream:

upstream speed = 8 - 2 = 6 kmph

Find the time to cover 1 km upstream:

6 km = 1 hour

1 km = 1/6 hour = 1/6 x 60 = 10 mins

Find the speed with going downstream:

downstream speed = 8 + 2 = 10 kmph

Find the time to cover 1 km downstream:

10 km = 1 hour

1 km = 1/10 hour = 1/10 x 60 = 6 mins

Find total time needed to cover 1 km to and back from the place:

Time needed = 10 + 6 = 16 mins

Find distance if time needed is 45 minutes:

16 mins = 1 km

1 min = 1/16 km

45 mins = 1/16 x 45 = 2.8 km

Answer: The place is 2.8 km away