AlgebraEasy–MediumTwo multiples of sums set equal
Algebra practice question
Five times the sum of a number and 1 is equal to three times the sum of the same number and 5. What is the number?
Answer: 5
Let the number be x: 5(x + 1) = 3(x + 5), so 5x + 5 = 3x + 15. Subtract 3x: 2x + 5 = 15, so 2x = 10 and x = 5.
Common wrong answers
- If you answered 2
- 2 comes from 5x + 1 = 3x + 5 — the multipliers must apply to the whole sums.
- If you answered 10
- 10 is 2x, one step short.
- If you answered -5
- −5 comes from 2x = −10, subtracting 15 from 5 the wrong way round.
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