A boat takes 6 hours to cover a certain distance on a lake where the water is still. It takes 5 hours to cover the same distance downstream in a river that flows at 2 km/hr. What is the distance?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 60 km
The distance is the same both times, so speed × time on the lake equals speed × time downstream. Let the boat’s speed in still water be \(b\) km/hr.
On the lake: distance \(=6b\)
Downstream: distance \(=5(b+2)\)
\(6b=5b+10\), so \(b=10\) km/hr
Distance \(=6\times10=60\) km
Check: downstream \(60\div12=5\) hours