What is a missing addend?

A missing addend is the unknown number in an addition, shown as a ? or an empty box. Addends are the numbers being added, and the total they make is the sum. In 9 + ? = 20, the 9 is one addend and the ? is the other. Take the known addend from the sum, 20 − 9 = 11, and the missing addend is 11.

How do you work out number bonds to 20?

Start from a bond to 10 you already know and give one part an extra ten. Since 4 + 6 = 10, both 14 + 6 and 4 + 16 make 20. So ? + 16 = 20 is quick: 16 is a ten and a 6, and the partner of 6 is 4. In the same way, ? + 7 = 20 needs 3 plus a ten, which is 13.

How can kids remember number bonds to 10?

Kids remember number bonds to 10 best as a picture rather than a list. Draw ten circles in two rows of five and colour some in: 7 coloured circles leave 3 white ones, so 7 and 3 make 10. Each bond also works both ways, so learning 2 + 8 gives you 8 + 2 as well.

Why does my child add the numbers instead of finding the missing part?

Most children have learned that + means “add what you see”, so 4 + ? = 10 turns into 4 + 10 = 14. Reading the problem aloud as a question helps: “4 and how many more make 10?” Then ask your child to put their answer in the gap and read the sum again. 4 + 14 is 18, not 10, so the slip shows itself.

Is there a free number bonds activity for a whole class?

Yes: all three levels load free in any browser on a tablet or laptop, and pupils start without an account or a download. On the board, draw 10 in a circle with two empty circles under it. Pupils take turns filling one circle while the class calls out the other, until every pair from 1 and 9 to 9 and 1 is up. To follow each pupil’s progress, the schools plan adds a teacher dashboard, priced per student.

Math practice · reimagined

Number Bonds Game

In this number bonds fighting game, a question mark replaces one part, and the whole is always 5, 10, 20 or a number from 11 to 19. Fill the gap first and your fighter swings; fill it faster and the hit lands heavier.

Ages 4–99+ · no download · plays in your browser · 23 languages

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What are number bonds?

A number bond is a pair of numbers that join to make a whole, such as 3 and 7, which make 10. Know the whole and one part, and the bond gives you the other part. Picture 10 crayons in a box, 4 red and the rest blue. Because 4 and 6 make 10, 6 are blue.

Every level of Number bonds

Example: ? + 3 = 10, with the gap first

The whole is 10 and one part is 3, so the ? stands for the other part.
The gap comes first this time, but that changes nothing: ? + 3 and 3 + ? hide the same number.
Take the part you know away from the whole: 10 − 3 = 7.
Check that 7 + 3 makes 10, then type 7 on the keypad.

Learn it step by step

A number bond is two little parts that snap together to make a whole. Here the whole is 10 (and sometimes 20), one part is shown, and the other part is hiding behind the ?. Your job is to find the hidden part.

Picture 10 fingers. If 6 of them are up, how many are folded down? Four — because 6 and 4 together make 10. So 6 + ? = 10 means the ? is 4. You can count up from the part you can see until you reach the whole: from 6 it's 7, 8, 9, 10 — that's 4 steps.

Knowing the pairs that make 10 by heart (1 and 9, 2 and 8, 3 and 7, 4 and 6, 5 and 5) is a superpower — it makes every bigger sum easier later. Find the missing part and type it.

Tips and common mistakes

Write 1 to 9, then 9 down to 1 beneath it. Each column makes 10: as the top number grows by one, the one below shrinks by one.
A common slip is answering for 10 when the whole is 20: ? + 6 = 20 needs 14, not 4. Read the number after the = sign first.
Clip 10 clothes pegs on a coat hanger for a make ten game. Slide some to one end, ask how many are at the other end, then swap roles.

How to play

Each sum has a gap, such as 4 + ? = 5 or ? + 16 = 20, and the gap can come first. Type the missing part on the keypad; the first right answer sends Garlic in, and speed adds damage. On the eleven-to-nineteen level, one part is always 10: 10 + ? = 17 wants the 7.

— Quick answers —

Number bonds: the short FAQ

What is a missing addend?: A missing addend is the unknown number in an addition, shown as a ? or an empty box. Addends are the numbers being added, and the total they make is the sum. In 9 + ? = 20, the 9 is one addend and the ? is the other. Take the known addend from the sum, 20 − 9 = 11, and the missing addend is 11.
How do you work out number bonds to 20?: Start from a bond to 10 you already know and give one part an extra ten. Since 4 + 6 = 10, both 14 + 6 and 4 + 16 make 20. So ? + 16 = 20 is quick: 16 is a ten and a 6, and the partner of 6 is 4. In the same way, ? + 7 = 20 needs 3 plus a ten, which is 13.
How can kids remember number bonds to 10?: Kids remember number bonds to 10 best as a picture rather than a list. Draw ten circles in two rows of five and colour some in: 7 coloured circles leave 3 white ones, so 7 and 3 make 10. Each bond also works both ways, so learning 2 + 8 gives you 8 + 2 as well.
Why does my child add the numbers instead of finding the missing part?: Most children have learned that + means “add what you see”, so 4 + ? = 10 turns into 4 + 10 = 14. Reading the problem aloud as a question helps: “4 and how many more make 10?” Then ask your child to put their answer in the gap and read the sum again. 4 + 14 is 18, not 10, so the slip shows itself.
Is there a free number bonds activity for a whole class?: Yes: all three levels load free in any browser on a tablet or laptop, and pupils start without an account or a download. On the board, draw 10 in a circle with two empty circles under it. Pupils take turns filling one circle while the class calls out the other, until every pair from 1 and 9 to 9 and 1 is up. To follow each pupil’s progress, the schools plan adds a teacher dashboard, priced per student.

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