A boat moves at 10 km/hr in still water. In summer the river flows at 2 km/hr, and in the monsoon it flows at 4 km/hr. How much more time does the boat take to go 24 km upstream in the monsoon than in summer?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1 hour
Upstream the river’s speed is taken away from the boat’s speed, so a faster river makes the upstream trip slower.
Summer: upstream speed \(=10-2=8\) km/hr; time \(\displaystyle =\frac{24}{8}=3\) hours
Monsoon: upstream speed \(=10-4=6\) km/hr; time \(\displaystyle =\frac{24}{6}=4\) hours
Extra time in the monsoon \(=4-3=1\) hour