At 11:00 the boat left point A to point B, located 30 km from A. After staying at point B at 2:40, the boat set off back

| July 3, 2021 | education

At 11:00 the boat left point A to point B, located 30 km from A. After staying at point B at 2:40, the boat set off back and returned to point A at 19:00. Determine (in km / h) the speed of the river if it is known that the boat’s own speed is 12 km / h.

The boat returned to point A after 19 – 11 = 8 hours.

Taking into account the parking at point B, the boat was on the way

8 – 2 2/3 = 5 1/3 hours.

Let us assume that the speed of the river is x km / h, then the boat was moving downstream at a speed of (12 + x) km / h, and against the current at a speed of (12 – x) km / h.

Let’s compose an equation according to the condition of the problem:

30 / (12 + x) + 30 / (12 – x) = 5 1/3 = 16/3,

(360 – 30x + 360 + 30x) / (12 – x²) = 16/3,

720 / (144 – x²) = 16/3,

16x² = 2304 – 2160,

16x² = 144,

x² = 9,

x = 3.

Answer: 3 km / h.



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.