Math · Stage 3
Solve age problems using the constant age difference
The age gap never changes — so one gap unlocks every 'how old now?', 'how old then?' and 'how old in the future?' question.
✦ Math📘 Stage 3 · S3⏱ ~10 min🧒 Ages 7–8★ Free to start
I can solve age problems by using the fact that the difference between two people's ages stays constant over time.
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Kavi's Age Puzzle 🎂
Kavi finds a riddle: "In 4 years I will be 12, and I am 5 years older than my cousin. How old is my cousin now?" "Don't panic," hoots Kavi. "The gap between us is 5 and it never changes — so I can slide time forward or backward and the gap stays put. That one steady number is the key that opens the whole puzzle!"
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What your child will learn
1Older age = younger age + the gapDraw the two ages as bars. The longer bar is just the shorter bar plus the gap. Kavi is 13, cousin is 8. The bond shows it: 8 (cousin) + 5 (the gap) = 13 (Kavi). Slide to see the two parts.
2Slide time — the gap stays putA puzzle tells you about a future or past year. Slide BOTH ages by the same number of years and the gap does not move, so you can read off the age you need. Puzzle: in 4 years Kavi is 12 and is 5 older than the cousin. Tap each card.
3The gap is the jump between themMark the younger age on the line, then jump up by the gap to land on the older age. To find a missing age, work out the gap first, then add it or subtract it. Try jumps of the gap along the line.
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A peek inside
Kavi is 13 and the cousin is 8. In 6 years, how old will each be, and what will the gap be?
gap = 13 − 8 = 5 · add 6 to both: 13 + 6 = 19, 8 + 6 = 14 · 19 − 14 = 5
Try this at home: Ravi is 14, his sister is 9. What is the gap? What will the gap be in 7 years?
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 3 · S3 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.