A number bond splits a number into two parts. Pick a target, then slide to split it — the two parts always add back to the whole. Learn the bonds to 10 and 20 off by heart.
To add a 2-digit number, start at the first number and hop along. Add the tens first (big +10 hops), then the ones (small +1 hops). Try 34 + 23: hop +10, +10, then +1, +1, +1.
1. Missing number: ☐ + 6 = 14. What is ☐? 8 — because 14 − 6 = 8.
2. Word problem: Vi An has 25 marbles and finds 18 more. How many now? 25 + 18 = 43 marbles.
3. Three numbers: 10 + 20 + 30 = ? 60 — add the tens: 1 + 2 + 3 = 6 tens.
4. Near doubles: 7 + 8 = ? (hint: 7 + 7 = 14) 15 — it's the double 7 + 7 = 14, then one more.
Adding is friendly: 3 + 8 gives the same answer as 8 + 3. So start with the bigger number and count on — it's faster. And 10 + 20 + 30 can be added in any order you like.
The bonds you know by heart — like 7 + 3 = 10 — are the shortcuts that turn big sums into quick ones.