Math · Stage 1
Reason that an age difference stays constant over time (an invariant)
The gap between two ages never changes — every year both people grow older by exactly the same amount.
✦ Math📘 Stage 1 · S1⏱ ~9 min🧒 Ages 5–6★ Free to start
I can reason that an age difference is constant over time; verify by adding the same years to both.
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Kavi and Little Cousin Tam 🎂
Kavi is 7 and cousin Tam is 5. "I'm 2 years older," says Kavi. "Will I always be 2 years older?" Next year Kavi is 8 and Tam is 6 — still 2 apart! The gap never changes, because every year both of them grow older by exactly 1. An age difference is an invariant — a number that stays the same no matter how much time passes.
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What your child will learn
1Older age = younger age + the gapKavi is 7, Tam is 5. The older age is the younger age plus the gap between them. The bond shows it: 5 (Tam) + 2 (the gap) = 7 (Kavi). Slide to explore.
2Jump forward in time — the gap stays!Add the same 3 years to BOTH ages. Kavi: 7 → 10. Tam: 5 → 8. Tap each card and check the gap between them.
3The gap is the jump on the linePut both ages on a number line and count the jumps from the younger age up to the older one — that jump is the gap. Now slide both ages along by the same amount: the jump between them stays exactly the same length.
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A peek inside
Kavi is 7 and cousin Tam is 5. How much older is Kavi? Will that change when they are both older?
gap now = 7 − 5 = 2 · in 3 years: 10 and 8 → 10 − 8 = 2
Try this at home: Kavi is 7, Tam is 5. How much older is Kavi? Will the gap change as they grow?
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 1 · S1 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.