The boat sailed 105 km between the piers along the river in 5 hours, and against the current in 7 hours.

| July 8, 2021 | education

The boat sailed 105 km between the piers along the river in 5 hours, and against the current in 7 hours. How many hours will the boat sail on the lake for 108 km?

We know the distance and time during which the boat sailed downstream and upstream. Let’s determine the speed of the boat along the river: 105/5 = 21 km / h.

Let’s calculate the speed of the boat against the current: 105/7 = 15 km / h.

Let us determine the speed of the river, let its speed be x km / h, then the equality is true:

21 – x = 15 + x → 2x = 21 – 15 → x = 3 km / h.

Knowing the speed of the boat downstream, against the current and the speed of the river, we determine the boat’s own speed: 21 – x = 15 + x → 21 – 3 = 15 + 3 = 18 km / h.

The lake has stagnant water, so the distance is 108 km. the boat will cover in:

108/18 = 6 hours.



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.