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Strictly speaking, your formula is wrong.

The correct one should be: 7×2÷[(6-5)/(6+5)]=7×2×(6+5).

The speed ratio of passenger ship and cargo ship is 6: 5. The two ships depart from Port A and Port B at the same time and meet at the midpoint of 7 kilometers.

Description: During the meeting time, the distance ratio between the two ships was 6: 5, with a difference of (7×2) kilometers.

In other words, the whole journey is divided into (6+5) shares on average, 6 shares for passenger ships and 5 shares for cargo ships.

The difference of (7×2) kilometers is (6+5) copies of (6-5).