The boat goes from one pier to another at a speed of 30 km / h, and returns back at a speed of 10 km / h more.

The boat goes from one pier to another at a speed of 30 km / h, and returns back at a speed of 10 km / h more. How long does it take for the boat to travel all the way back and forth if the distance between the marinas is 240 km?

Let’s determine the speed of the boat on the way back.
30 + 10 = 40 km / h.

Let’s determine how long the boat sailed at a speed of 30 km / h.
240:30 = 8 hours.

Let’s determine how long the boat sailed at a speed of 40 km / h.
240: 40 = 6 hours.

Let’s determine how much time was spent on the way back and forth.
8 hours + 6 hours = 14 hours.

Answer: the whole way back and forth took 14 hours.