Advanced Math practice question

Answer: 80

(3 + 1)(3 − 1) = 3² − 1 = 8, and 8(3² + 1) = 8 × 10 = 80. (In general (x + y)(x − y)(x² + y²) = x⁴ − y⁴ = 81 − 1.)

Common wrong answers

If you answered 40

40 is 4 × 10, dropping the factor (3 − 1) = 2.

If you answered 64

64 is 4 × 2 × 8, taking 3² + 1² as 8.

If you answered 82

82 adds 1 instead of subtracting: 3⁴ + 1.

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