Algebra practice question

Answer: 5

Let the number be x: 3(x + 2) = 21. Divide by 3: x + 2 = 7, so x = 5.

Common wrong answers

If you answered 7

7 is x + 2, one step short.

If you answered 9

9 comes from x + 2 = 21 − 3 = 18 or a similar slip; divide by 3 first.

If you answered 19

19 comes from 3x + 2 = 21 — the 3 must multiply the whole sum, including the 2.

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