Addition within 20, step by step
Addition within 20 is where children move past counting fingers and start using strategies.
The question
8 + 4
8+4
8+2=10
4=2+2
10+2=12
- 8 + 4. Both are under ten and the answer is not, so the crossing is the whole of the work — and ten is the easy place to cross at.
- 8 is 2 short of ten. Take that 2 out of the 4: 8 + 2 = 10, and 2 of the 4 is still to come.
- Ten and 2 is easy to see: 8 + 4 = 12.
How it works.
- 01
8 + 4. Both are under ten and the answer is not, so the crossing is the whole of the work — and ten is the easy place to cross at.
- 02
8 is 2 short of ten. Take that 2 out of the 4: 8 + 2 = 10, and 2 of the 4 is still to come.
- 03
Ten and 2 is easy to see: 8 + 4 = 12.