A man can swim along the stream at 3 km/h and against the stream at 2 km/h. How long will he take to swim 7 km in still water?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2 h 48 min
Along the stream the current adds to the man’s own speed, and against it the current takes away the same amount; so his speed in still water is the average of the two speeds.
Speed in still water \(\displaystyle =\frac{3+2}{2}=2.5\) km/h
Time for 7 km \(\displaystyle =\frac{7}{2.5}=2.8\) h
\(0.8\) h \(=0.8\times60=48\) min, so the time is 2 h 48 min