The distance between A and B, located on the same bank of the river, the boat sails in 3 hours along the river

The distance between A and B, located on the same bank of the river, the boat sails in 3 hours along the river, the same distance the raft will sail in 12 hours along the river. How long will it take for the boat to sail this distance against the current?

Let us assume that the boat’s own speed is x km / h, and the current speed is y km / h.

The boat will go downstream at a speed of x + y km / h and in 3 hours it will cover 3 * (x + y) km.

The raft moves along the river at the speed of the current, which means that in 12 hours the raft will pass 12 * km.

We get the equation:

3 * (x + y) = 12 * y,

x + y = 4 * y,

x = 3 * y.

Since the speed of the boat against the current is equal to x – y km / h, it is equal to:

3 * y – y = 2 * y km / h.

Therefore, the distance of 12 * y the boat against the current will pass for:

12 * y: 2 * y = 6 hours.

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