Advanced Math practice question

Answer: 8

Substitute x = 5: f(5) = 3(5) − 7 = 15 − 7 = 8. The trap is subtracting before multiplying (getting 3·(5−7) = −6); the order of operations requires multiplying 3·5 first.

Common wrong answers

If you answered 15

You substituted and multiplied 3 · 5 = 15 but never subtracted the 7. f(5) = 15 − 7 = 8.

If you answered 22

You added 7 instead of subtracting it. The rule is 3x − 7, so f(5) = 15 − 7 = 8.

If you answered -6

You subtracted before multiplying: 3(5 − 7) = −6. Order of operations means multiply 3 · 5 first, then subtract 7, giving 8.

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