The boat sailed 72 km along the river. How long did it take it if the boat’s own speed was 21

The boat sailed 72 km along the river. How long did it take it if the boat’s own speed was 21 km / h and the river’s speed was 3 km / h?

First you need to find the speed at which the boat was sailing in the indicated direction.

Since he was swimming with the flow, add another 3 km / h (current speed) to his own speed.

21 + 3 = 24 km / h.

We find the time of movement of the boat.

We divide 72 km by the speed obtained earlier.

72/24 = 3 hours.

Answer: This trip took the boat 3 hours.