Unit 6 · Algebra
Sum of Ages — Find the Values
Lesson 1 of 24
When two ages add to a total and one person is a fixed number of years older, let the younger age be x — the elder is x + 3 and their sum gives you one quick equation.
Sum-and-difference age items appear in the very-easy band of Selective MR — solid introduction to one-variable algebra before timeline age puzzles.
The examiner checks whether you can define two unknowns with one letter using a stated age gap, then use the combined total to solve.
Two siblings’ ages sum to a given number this year, with a fixed year gap between them. You find each current age.
Best approach: Let younger = x, elder = x + gap. Write x + (x + gap) = total, solve for x, then state both ages. Quick check: difference should match the gap.
Question
The sum of the ages of an elder sister and her younger sister is 27 years this year, and the elder sister is 3 years older than her younger sister. How old is each of the elder sister and her younger sister this year?
Select an answer to see the explanation.
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