Question

Small tug boats pull cruise ships up and down rivers to prevent them from grounding. Cruise ships anchor 22 km away from the river port. A tug boat can travel 20 km downstream in the same time it takes it to travel 10 km upstream. If the speed of the current is 5 km/h, calculate the time it takes for the tug boats to travel upstream from the cruise ship to the river port.

Answer 1

2.2 hr

Explanation:

Let the speed of the boat in km/h be x.

Then, the speed downstream is (x+5), and the speed upstream is (x-5).

We know the speed downstream is twice the speed upstream, so

`x+5=2(x-5) \\ \\ x+5=2x-10 \\ \\ x=15`

This means the speed upstream is 10 km/h. Thus, to travel 22 km, it will take 2.2 hrs.