Math · Stage 4
Use factor pairs and doubling/halving for fast multiplication
Halve one factor and double the other to land on an easy table, or split a factor into a friendly pair — two China-fast ways to multiply big numbers in your head.
✦ Math📘 Stage 4 · S4⏱ ~10 min🧒 Ages 8–9★ Free to start
I can multiply quickly by halving one factor and doubling the other, and by splitting a factor into a friendly factor pair.
📖
Kavi's Seesaw Trick ⚖️
Kavi stares at 16 × 5 and grins. "Too slow the long way!" hoots Kavi. "I halve one side and double the other — 16 drops to 8, the 5 jumps to 10 — and now it's just 8 × 10 = 80 ⚡. Same answer, easier numbers!"
🎓
What your child will learn
1Doubling and halving are a seesawDoubling and halving are opposites that balance. Here the whole 24 splits into 12 and 12, so double 12 is 24 and half of 24 is 12. Tap more ▶ and ◀ less to split the whole into two equal parts.
2Land on the easy ten-times tableTry 16 × 5. Nobody likes ×16! So halve the 16 to 8 and double the 5 to 10 → it becomes 8 × 10. The lit numbers are the easy tens you land on: 10, 20, 30, 40…
3×4 is a double-doubleA factor can be split into a pair: 4 = 2 × 2. So to multiply by 4, double twice. Try 15 × 4: double 15 is 30, double 30 is 60. The lit numbers are the fours.
4×6 is ×2 then ×3Split 6 = 2 × 3. To multiply by 6, double first, then times three. Try 12 × 6: double 12 is 24, then 24 × 3 = 72. The lit numbers are the sixes.
🔍
A peek inside
Kavi needs 16 × 5 fast with the seesaw ⚖️.
halve 16 → 8, double 5 → 10, so 8 × 10
Try this at home: Seesaw to ×10: 18 × 5 → halve 18 = __ , double 5 = 10 · so 18 × 5 = __
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.