The boat went with the current for 3.5 hours, then 4.2 hours against the current and covered 159.67 km.

| April 5, 2021 | education

The boat went with the current for 3.5 hours, then 4.2 hours against the current and covered 159.67 km. Find the speed of the boat if the speed of the river is 2.9 km / h.

Let the boat’s own speed be x km / h, then the speed of the boat along the river is (x + 2.9) km / h, and the speed of the boat against the river is (x – 2.9) km / h. The boat covered a distance of 3.5 (x + 2.9) kilometers in 3.5 hours along the river, and 4.2 (x – 2.9) kilometers against the river in 4.2 hours. According to the condition of the problem, it is known that the entire path of the boat is equal to (3.5 (x + 2.9) + 4.2 (x – 2.9)) kilometers or 159.67 kilometers. Let’s make an equation and solve it.

3.5 (x + 2.9) + 4.2 (x – 2.9) = 159.67;

3.5x + 10.15 + 4.2x – 12.18 = 159.67;

7.7x – 2.03 = 159.67;

7.7x = 159.67 + 2.03;

7.7x = 161.7;

x = 161.7: 7.7;

x = 21 (km / h).

Answer. 21 km / h



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