Math · Stage 6
Percentage shortcuts (10%, 5%, 1% build-up) mentally
No calculator needed. Find the three building blocks — 10% (÷10), 5% (half of 10%) and 1% (÷100) — then add and double them to build any percentage in your head.
✦ Math📘 Stage 6 · S6⏱ ~12 min🧒 Ages 10–12★ Free to start
I can find 10%, 5% and 1% and build other percentages mentally.
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Kavi's Night-Market Discount ⚡
A stall offers 15% off a $80 jacket and the queue is long. Kavi never reaches for a calculator! "10% of 80 is 8 — just divide by ten. 5% is half of that, 4. So 15% off is 8 + 4 = 12 dollars off," Kavi hoots. Three tiny building blocks — 10%, 5% and 1% — can build any percentage in your head.
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What your child will learn
1Find 10%, 5% and 1% firstEvery mental-percentage trick starts with three easy blocks. 10% = divide by 10 (slide each digit one place right). 5% = half of 10%. 1% = divide by 100 (two places right). Get these three and you can build the rest. Tap a row.
2The three blocks, side by sideHere are the three building blocks of 200. Notice the pattern: 10% is the biggest, 5% is exactly half of it, and 1% is the smallest. Every other percentage is made by stacking copies of these.
3Build any percentage by adding blocksOnce you have 10%, 5% and 1%, add and double them to build the percentage you need. 20% = two 10%s. 15% = 10% + 5%. 25% = 10% + 10% + 5%. 12% = 10% + 1% + 1%. Tap a row to see the blocks.
4Detective: is the answer sensible?Because every percentage is built from blocks you can check any answer fast. 10% can never equal the whole number, and 5% must be smaller than 10%. If the blocks don't add up, the answer is wrong. Tap a row.
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A peek inside
Find 15% of 80 mentally.
10% of 80 = 8; 5% is half of that = 4; 15% = 8 + 4
Try this at home: Find the three blocks of 70: 10% = __ · 5% = __ · 1% = __
Ready to play and learn?
Start the free interactive lesson, or print the handout for screen-free play.
Part of Math · Stage 6 · S6 on KAVI Academy — a secular, whole-child learning platform for ages 5–12.