Advanced Math practice question

Answer: 63/8 or 7.875

Let u = 2ˣ; then u + 1/u = 65/8 gives 8u² − 65u + 8 = 0, so u = 8 (since x > 0) and u − 1/u = 8 − 1/8 = 63/8.

Common wrong answers

If you answered 8

8 is 2ˣ alone.

If you answered 1/8

1/8 is 2⁻ˣ alone.

If you answered 65/8

65/8 is the given sum.

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