Simple But Perfect Tube Puzzle

SPOTTED the following serial number on a Central Line carriage: 72173.

As usual, each number should be used once, and once only, and must be added, subtracted, multiplied or divided to make a balanced equation.
The simplest solution is also a perfect solution, ie one that uses the numbers in the order they appear.
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My solution: 7 + 2 + 1 = 7 + 3