Math · Stage 3
Fast ×4, ×8 and ×9
×4 is double-double, ×8 is double-double-double, and ×9 is ten times minus one group — three China-fast tricks.
✦ Math📘 Stage 3 · S3⏱ ~10 min🧒 Ages 7–8★ Free to start
I can fast multiply by 4 and 8 (doubling) and by 9 (x10 minus x1).
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Kavi's Speed Tricks ⚡
Kavi doesn't memorise every fact the slow way! "Watch," hoots Kavi. "For ×4 I double twice. For ×8 I double three times. And for ×9 I take ten groups and give one back ⚡!"
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What your child will learn
1Doubling is the engineEvery fast trick starts with doubling — adding a number to itself. Here 8 + 8 = 16, so double 8 is 16. Tap more ▶ and ◀ less to split the whole into two equal parts.
2×4 = double, then double againTo multiply by 4, double the number twice. Try 6 × 4: double 6 is 12, double 12 is 24. The lit numbers are the fours: 4, 8, 12, 16, 20, 24…
3×8 = double three timesMultiplying by 8 is doubling three times. Try 7 × 8: double 7 is 14, double 14 is 28, double 28 is 56. The lit numbers are the eights.
4×9 = ten groups, give one backFor ×9, take ×10 (easy — just add a zero) then subtract one group. Try 6 × 9: 6 × 10 = 60, then take away 6 → 54. The lit numbers are the nines.
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A peek inside
Kavi needs 6 × 4 fast using double-double ⚡.
double 6 → 12, double 12 → 24
Try this at home: Double-double for ×4: double 5 = __ , double again = __ · so 5 × 4 = __
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.