Simple Perfection

THE following serial number from a Central Line carriage makes for a Tube Puzzle with a perfect but simple solution: 91731.
As usual, each number should be used once and once only, and must be added, subtracted, multiplied or divided to make a balanced equation. A perfect solution is one that uses the digits in the order printed.
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My solution: 9 + 1 = 7 + 3 (÷ 1)