The boat covered the distance between the two piers, moving along the river, in 4.5 hours.

The boat covered the distance between the two piers, moving along the river, in 4.5 hours. On the way back, he spent 6.5 hours. The speed of the river is 4 km / h. Find the distance between the marinas.

1. Let’s solve the problem through the equation. Let the required distance be x km. Consequently, when moving along the river, the boat moved at a speed. x / 4.5 km / h, and when moving against the current at a speed of x / 6.5 km / h.

2. Since the speed of the current is 4 km / h, therefore the boat’s own speed is x / 4.5 – 4 km / h or x / 6.5 + 4 km / h.

Let’s make the equation:

x / 4.5 – 4 = x / 6.5 + 4;

6.5 * x – 4.5 * x = 8 * 6.5 * 4.5;

2 * x = 8 * 6.5 * 4.5;

x = 117.

Answer: the required distance is 117 km.