Advanced Math practice question

Answer: 10

(x + y)² − (x − y)² = 4xy. So 49 − 9 = 40 = 4xy, and xy = 10.

Common wrong answers

If you answered 20

20 halves 40 instead of dividing by 4; the difference of the two squares is 4xy.

If you answered 29

29 is (49 + 9)/2 = x² + y², not xy.

If you answered 40

40 is 4xy, one step short.

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