Advanced Math practice question

Answer: 5/2 or 2.5

Write 81 as a power of 3: 81 = 3⁴. Then 2x − 1 = 4, so x = 5/2.

Common wrong answers

If you answered 2

2 comes from 2x = 4, forgetting the −1 in the exponent.

If you answered 4

4 is the exponent that 3 must have, not x itself.

If you answered 3/2

3/2 comes from 2x − 1 = 2, using 81 = 9² without converting to base 3.

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