Puzzle 68 - Solution

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 The puzzle was

  The sum of two numbers is 10. The product of these numbers is 20. What is the sum of their reciprocals?

Instead of writing complicated equations, we can use a simple tweak. 

If the numbers are x and y, then sum of their reciprocal is 1/x+1/y = (x+y)/xy

Since we have both sum - x+y and product - xy of the numbers, the answer is 10/20 = 1/2

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