A man can row 10 km/h in still water. When the river is running at a speed of 4.5 km/h, then it takes him 2 h to row to a place and comes back to the initial point. How far is the place (in km) (rounded off to two decimal places)?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 7.98
Speed in still water = 10 km/h
Speed of stream = 4.5 km/h
Downstream speed
= 10 + 4.5
= 14.5 km/h
Upstream speed
= 10 − 4.5
= 5.5 km/h
Let the distance be x km.
Time downstream + Time upstream = 2 h
x/14.5 + x/5.5 = 2
(5.5x + 14.5x)/(14.5 × 5.5) = 2
20x/79.75 = 2
20x = 159.5
x = 159.5/20
x = 7.975 km