Anuj can row 8 kmph in still water If in a river running at 2 km an hour it takes him 40 minutes to ...........

Quantitative Aptitude (CDS) Boats and Streams

Anuj can row 8 kmph in still water. If in a river running at 2 km an hour, it takes him 40 minutes to row to a place and back, how far off is the place?

4 km

3.5 km

5km

2.5km

Explanation:

Speed downstream = (8 +2)kmph = 10 kmph
Speed upstream = (8 - 6)kmph = 6 kmph
Let the required distance be x km.
Then, (x/10 + x/6) = 40/60
3x+5x = 4/6×30
8x = 20
x = 20/8
x = 2.5 km
Hence, the required distance is 2.5 km.