Brain Exercise

I RECKON keeping the brain active must help when it comes to playing chess, or at least it does no harm.

That is why on London tube trains I like to solve what I call Tube Puzzles.

One I saw today on the Northern Line looked at first glance to be easy, but proved surprisingly tricky, at least for me.

The carriage had the serial number 53576.

As usual, each number should be used once, and once only, and must be added, subtracted, multiplied or divided to make a balanced equation.
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My solution: 5 + 5 = 7 + (6 - 3)