Algebra practice question

Answer: D. 23

Multiply both sides by 3: x − 5 = 18. Then add 5 to both sides: x = 23. Check: (23 − 5)/3 = 18/3 = 6. Choice A comes from adding 5 to 6 without first multiplying by 3. Choice B comes from subtracting 5 from 18 instead of adding it (undoing the subtraction incorrectly). Choice C comes from multiplying by 3 but forgetting to undo the −5.

Why the other answers are wrong

A. 11

You added 5 to 6, but you have to undo the division by 3 first: multiply both sides by 3 to get x − 5 = 18.

B. 13

After multiplying by 3 you got x − 5 = 18, then subtracted 5 instead of adding it; to undo −5 you add 5, giving 23.

C. 18

You multiplied both sides by 3 to get x − 5 = 18 but stopped there — that's x − 5, not x, so add 5 to finish.

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