The motor boat sailed some distance along the river in 2 hours, and the raft in 8 hours.

The motor boat sailed some distance along the river in 2 hours, and the raft in 8 hours. How long will the boat take on the return trip?

As you know, the speed of the raft depends on the speed of the river.
in this case, we assume that the speed of the raft = the speed of the river.
Since the boat was sailing along the river, then its speed is equal to the sum of its own speed and the speed of the river. Let’s write the entire distance as x.
We get:
х / 8 – current speed.
x / 2 is the speed of the motor boat along the river.
x / 2 – 2 * x / 8 – speed of the motor boat against the river flow.
We get:
x / x / 4 = x * 4 / x = 4 hours (Time of the motor boat on the way back.)