Math · Stage 5
Multiply by 25 and 125 by scaling (x100/4, x1000/8)
25 is one quarter of 100 and 125 is one eighth of 1000 — so to multiply by 25, multiply by 100 then divide by 4; to multiply by 125, multiply by 1000 then divide by 8. A China-fast way to do these in your head.
✦ Math📘 Stage 5 · S5⏱ ~10 min🧒 Ages 9–10★ Free to start
I can multiply by 25 and by 125 using the quarter-of-100 and eighth-of-1000 shortcuts.
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Kavi's Quarter-and-Eighth Trick ⚡
"×25 looks scary," hoots Kavi, "so I never do it the long way!" Kavi knows a secret: 25 is one quarter of 100 and 125 is one eighth of 1000. "So I scale up to a friendly round number first, then share it out — and the answer pops out in my head ⚡."
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What your child will learn
1Count by 25 up to 100Hop in 25s: 25, 50, 75, 100. It takes exactly four hops to reach 100 — so four 25s make 100, which means 25 is one quarter of 100.
2One quarter of 100 is 25Here is 100 split into 4 equal parts. Each part is worth 25. Shade one part and you have one quarter — 1/4 — of 100, which is 25.
3Count by 125 up to 1000Now hop in 125s: 125, 250, 375, 500, 625, 750, 875, 1000. It takes eight hops to reach 1000 — so eight 125s make 1000, which means 125 is one eighth of 1000.
4One eighth of 1000 is 125Here is 1000 split into 8 equal parts. Each part is worth 125. Shade one part and you have one eighth — 1/8 — of 1000, which is 125.
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A peek inside
Multiply 32 × 25 the fast way (×100, then ÷4).
32 × 100 = 3200, then 3200 ÷ 4 = 800
Try this at home: Multiply by 25 (×100 then ÷4): 8 × 25 = __ · 12 × 25 = __ · 40 × 25 = __
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 5 · S5 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.