Math · Stage 4
Use divisibility tests to check calculations
Quick tests for 2, 5, 3 and 9 let you judge in seconds whether an answer could possibly be right — no long division needed.
✦ Math📘 Stage 4 · S4⏱ ~11 min🧒 Ages 8–9★ Free to start
I can use divisibility tests for 2, 5, 3 and 9 as quick checks, and use them to judge whether a calculation could be correct.
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Kavi the Detective 🔍
A friend hoots, "Kavi, is 3 × 17 = 50?" Without dividing anything, Kavi says "No!" in one second. "A ×3 answer must pass the digit-sum test — and 50 fails it 🔍." Today you become a calculation detective too!
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What your child will learn
1÷2 and ÷5 live in the last digitYou don't need to divide — just look at the final digit. If it's 0, 2, 4, 6 or 8 the number is divisible by 2 (even). If it's 0 or 5 the number is divisible by 5. Tap a row to hear it.
2Numbers divisible by 3The lit numbers are the multiples of 3: 3, 6, 9, 12, 15, 18… You can't tell a ÷3 number from its last digit — so we need a different trick: add the digits.
3÷3 and ÷9 live in the digit sumAdd all the digits. If the total is a multiple of 3, the number is divisible by 3. If the total is a multiple of 9, the number is divisible by 9. (Every ÷9 number is also ÷3 — but not the other way round.)
4Numbers divisible by 9The lit numbers are the multiples of 9: 9, 18, 27, 36, 45… Add the digits of each and you always get 9 — the signature of a nine.
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A peek inside
Is 90 divisible by 5? Use the last-digit test.
last digit is 0 → in the 5× table
Try this at home: Last-digit check: Is 70 divisible by 5? __ · Is 64 divisible by 2? __
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 4 · S4 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.