Early MathNumber bonds to 20
Name: Date:
Write the number that is missing from each bond.
12010
22011
3201
42013
52012
62015
7205
8209
92019
10207
Number bonds to 20 worksheets
Every bond on this page is a bond of twenty. One part is shown and the other is blank, so the whole sheet is the same question asked about nineteen different splits. Free printable sheets, with an answer key.
If they get stuck
Number bonds to 20
The answer key prints on a separate page.
What's on this sheet
One whole, all the way down. The mixed number bonds sheet next door keeps five and ten in a child's hands while twenty is being learned, which is the right sheet for that week; this is the one for the week after, when twenty is the thing being committed to memory and a mixed page would keep interrupting it.
Why this sheet works
Nineteen splits is all there are — 1 and 19 through 19 and 1 — so a page of eight is nearly half of everything twenty can be made of, and two pages cover the lot. That is the whole reason a bond sheet is worth printing twice: the set is small enough to finish.
How this one works
10 and ? make 20
••••••••••••••••••••
whole:20
••••••••••|••••••••••
10 + 10 =20
20 − 10 =10
0 +20=20
1 +19=20
2 +18=20
3 +17=20
4 +16=20
5 +15=20
- The whole is 20 and it never changes — the two parts just share it out. So this is not really a sum: it is asking what is left of 20 once 10 is taken.
- 10 in one part leaves 10 in the other: 10 and 10 make 20.
- And because the two parts are the same, this one is smaller than most: 10 + 10 = 20 and 20 − 10 = 10, and that is the whole family. Swapping equal parts changes nothing.
- Move one across and the other moves the same amount the other way — the whole is fixed, so the parts can only trade. That is why the whole set of bonds for 20 is one thing to remember rather than 21.