10 printable sets · answer key on every set

Addition Within 20 Worksheets

CCSS 1.OA.C.6
20 problems per set
Answer key included

What this skill is

Adding within 20 in cases that do not cross a ten — 12 + 3, 5 + 4.

When it comes up: Early first grade.

The mistake to watch for

Adding the tens digit into the ones, so 12 + 3 becomes 6 (1 + 2 + 3).

How to help

Write the teen number as 10 + 2 before adding. The ten sits still while the ones change.

Next: Addition with regrouping to 20.

A worked example

Try 9 + 6. Count on from 9: 10, 11, 12, 13, 14, 15. Or use a double: 6 + 6 = 12, and 9 is 3 more than 6, so 12 + 3 = 15.

Words to know

add: To put numbers together to find how many in all.
sum: The answer you get when you add.
total: All of the things added together.
double: Two times as much. The double of 6 is 12.
equal: The same amount. The sign = means "is equal to".

Practice

Add.

Showing Set 1 · 20 problems

10 + 4 =
10 + 6 =
17 + 1 =
4 + 4 =
11 + 2 =
7 + 12 =
18 + 1 =
3 + 11 =
4 + 15 =
10 + 5 =
2 + 13 =
1 + 2 =
10 + 8 =
1 + 11 =
2 + 5 =
2 + 15 =
12 + 3 =
10 + 1 =
10 + 3 =
14 + 3 =

Download this set20 problems · answer key included PDF

Answer key

All 10 sets

Each set is a different list of 20 problems with its own answer key. Use the buttons above to look at one on this page, or download any of them as a PDF.

How these sheets were made

Problems are generated for each set and checked against 1.OA.C.6 before the sheet is built — no duplicates, and every problem falls inside the standard's number range.