Number bonds to 20

Instant recall of bonds underpins all fast arithmetic in the 7+. James has bonds to 10 secure — this extends them to 20.

In kid words

A number bond is two numbers that click together to make a total. You already know the pairs that make 10. Now we find all the pairs that make 20 — and there's a clever shortcut.

Worked example

The shortcut: if you know a bond to 10, you know the matching bond to 20.

You know 6 + 4 = 10. So just add ten to one part: 16 + 4 = 20. And 6 + 14 = 20.

Bond to 10	Becomes a bond to 20
1 + 9	11 + 9 · 1 + 19
2 + 8	12 + 8 · 2 + 18
5 + 5	15 + 5 · 10 + 10
7 + 3	17 + 3 · 7 + 13

Exercises

📄 Printables: worksheet · flashcards.

Warm-up · bonds to 10 (quick-fire)

Call out a number 0–10; he says its partner to 10. Aim for fast and automatic.

Core · make 20

Fill the gap:

14 + __ = 20
__ + 5 = 20
20 = 8 + __
13 + __ = 20

Answers

1. 6 2. 15 3. 12 4. 7

Stretch · subtraction is a bond too

Show that bonds work backwards: if 13 + 7 = 20, then 20 − 7 = ? and 20 − 13 = ?

Answers

20 − 7 = 13 · 20 − 13 = 7. Same three numbers, different job!

Play it

Games that build this Make 20 snap: with playing cards (10s as 10, picture cards removed, 20 = two cards summing to 20), shout when two cards make 20.
Bond ping-pong: you say a number, he fires back its partner to 20, then he sets one for you.
Online: "Hit the Button" → number bonds (see references).
On a tablet: 🧮 James's Maths Game → Adding / Mix it up.

Watch for (grown-up note)

Goal is recall, not counting on fingers. If he's counting up each time, slow down and over-learn bonds to 10 first, then use the "+10" shortcut. Two minutes of quick-fire daily beats one long session.

Words we used

Glossary: number bond, double.

Note for the log

In log/, jot: recalling bonds to 20 instantly, or still counting on? Which pairs are sticky?