Math · Stage 5
Square numbers ending in 5
A two-digit number ending in 5 squares in one breath: multiply the tens digit by the next number, then just write 25 on the end — a China-fast mental-maths trick.
✦ Math📘 Stage 5 · S5⏱ ~10 min🧒 Ages 9–10★ Free to start
I can square a two-digit number ending in 5 using the tens-times-next shortcut.
📖
Kavi's One-Breath Square ⚡
"Watch me square 35 without writing a thing," hoots Kavi. "I take the tens digit 3, times the next number 4 — that's 12 — then I just stick 25 on the end. 1,225! Every number ending in 5 hides this trick ⚡."
🎓
What your child will learn
1Every 'ends-in-5' number is tens + 5A two-digit number ending in 5 is just some tens and a 5. Here is 35 = 30 + 5. That 5 on the end is the secret — it is the same for every number in this family, and 5 × 5 is always 25.
2Look: the square always ends in 25Build 625 — that is 25 × 25. See the 5 ones and 2 tens? Together they are the 25 on the end. The 6 hundreds in front come from 2 × 3 — the tens digit (2) times the next number (3).
3Tens × next, then write 25Square 45. The tens digit is 4 and the next number is 5, so 4 × 5 = 20. Put that in front as hundreds → 2000, then add the 25 tail. Tap Step → to build 2000 + 25.
4Bigger tens, exactly the same trickNow 75. Tens digit 7, next number 8, so 7 × 8 = 56 → 5600, then the 25 tail. Tap Step → to build 5600 + 25.
🔍
A peek inside
Square 35 with the shortcut.
tens 3 × next 4 = 12, then write 25 on the end
Try this at home: Square with the shortcut: 15² = __ (1 × 2 = __, then 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.