Math · Stage 4
Multiply a two-digit number by 11 — the neighbour-sum shortcut
Split the two digits apart, drop their sum in the middle, and ×11 is done in your head — a true China-fast mental trick.
✦ Math📘 Stage 4 · S4⏱ ~10 min🧒 Ages 8–9★ Free to start
I can multiply a two-digit number by 11 using the neighbour-sum shortcut.
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Kavi's Eleven Trick ✨
"Watch this!" hoots Kavi. "To multiply by 11, I pull the two digits apart and drop their sum right in the middle. 23 × 11 → 2 _ 3 → the middle is 2 + 3 = 5 → 253 ✨. No long working at all!"
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What your child will learn
1The 11 table repeats its digitEleven is a friendly number. Count by 11 and watch the lit numbers: 11, 22, 33, 44 … — each single-digit answer just doubles the digit. Tap along and see the pattern up to 99.
2×11 is ×10 and one more groupHere's the secret. 23 × 11 means 23 × 10 plus one more 23. That's 230 + 23. Tap Step → to add them. Watch the tens column: 3 + 2 = 5 — the neighbour sum appears all by itself!
3Pull apart, drop the sum in the middleBuild 253. Read it as three parts: the first digit is the tens of 23 (that's 2), the last digit is the ones of 23 (that's 3), and the middle is their sum 2 + 3 = 5. Two digits apart, neighbour-sum between.
4If the middle makes 10+, carry oneWhat if the neighbour sum is 10 or more? Take 76 × 11. The middle would be 7 + 6 = 13 — too big for one slot! The extra ten carries left. Check with ×10 + one more: 760 + 76. Tap Step →.
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A peek inside
Kavi needs 23 × 11 using the neighbour-sum trick ✨.
keep 2 _ 3 · middle = 2 + 3 = 5
Try this at home: Neighbour-sum for ×11: 14 → 1 _ 4 , middle = 1 + 4 = __ · so 14 × 11 = __
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.