Math · Stage 3
Add and subtract near-round numbers by compensation, then adjust back
348 + 99? Jump to the friendly hundred — 348 + 100 = 448 — then give 1 back → 447. Round, then adjust.
✦ Math📘 Stage 3 · S3⏱ ~12 min🧒 Ages 7–8★ Free to start
I can add and subtract near-round numbers by compensation: a friendly ten or hundred, then adjust back.
📖
Kavi's One-Step Shortcut 🦉
Kavi needs 348 + 99. "Ninety-nine is almost a hundred!" he hoots. So he adds the friendly 100 first — 348 + 100 = 448 — then gives 1 back → 447. "Round it, then adjust," winks Kavi. "Faster than carrying every column!"
🎓
What your child will learn
1Friendly tens have a tiny gapA round ten is easy to add. Tap more ▶ / ◀ less and watch the two parts always make 10. See that 9 is just 1 short of 10, and 8 is 2 short.
2Adding a hundred just bumps one blockBuild 347. Now tap + on the 100s — one flat appears and you have 447. Adding a friendly hundred is one easy move.
3The long way vs the fast wayHere is 523 − 198 the column way — tap Step → and watch all that borrowing. It works, but it is slow.
🔍
A peek inside
Kavi works out 348 + 99 🦉.
99 = 100 − 1 → 348 + 100 = 448 → give 1 back → 448 − 1
Try this at home: Add by compensation: 475 + 99 = __ (add 100, then give 1 back)
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.