(19+17)(19-17)

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• A 78
• B 77
• C 72
• D 79

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Answer: C. 72

Use the identity (a + b)(a - b) = a^2 - b^2, or just work out the brackets: 19 + 17 = 36 and 19 - 17 = 2, so 36 x 2 = 72.

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