Adding full tens
Adding full tens works just like adding small numbers: 30 + 40 is 3 tens plus 4 tens, which makes 7 tens, or 70. Children also solve missing-number problems such as 40 + __ = 100.
How to solve this
- When adding a full ten to a number, only the tens digit changes — the ones digit stays the same.
- Split the addition: add the tens part first, then bring the ones digit across unchanged.
- Check by working backwards: subtract the ten you added and you should get the original number.
Examples
30 + 20 = ?
50
60 + 10 = ?
70
Practice problems with answers
Solve these problems on paper or out loud, then check the answer key. The online practice and the printable worksheet give a new set every time.
- ___ + 10 = 20
- 30 + 70 = ___
- 30 + ___ = 50
- 30 + ___ = 40
- 30 + ___ = 60
- 20 + 70 = ___
- 10 + ___ = 90
- 20 + ___ = 80
Show answers
- 10
- 100
- 20
- 10
- 30
- 90
- 80
- 60