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Sum equals product

3 and 1.5 are a special pair of numbers, as 3+1.5=4.5 and 3×1.5=4.5 so 3+1.5=3×1.5.
Given a number a, can you find a number b such that a+b=a×b?

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If you enjoyed this puzzle, check out Sunday Afternoon Maths XXI,
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