Addition bridging ten
You learn additions that cross ten by filling up to exactly ten first.
How to work it out
- Split the second number to land on ten.
- Add to ten first.
- Then add the rest.
A worked example
7 + 8
- Split 8 into 3 and 5, because 7 + 3 = 10.
- Add the 3 first: 10.
- Then add the 5: 10 + 5 = 15.
More examples
9 + 4
- Split 4 into 1 and 3, because 9 + 1 = 10.
- Add the 1 first: 10.
- Then add the 3: 10 + 3 = 13.
6 + 7
- Split 7 into 4 and 3, because 6 + 4 = 10.
- Add the 4 first: 10.
- Then add the 3: 10 + 3 = 13.
8 + 5
- Split 5 into 2 and 3, because 8 + 2 = 10.
- Add the 2 first: 10.
- Then add the 3: 10 + 3 = 13.
Try it yourself
9 + 4 =
7 + 9 =
Watch out
You split the number the wrong way: for 7 + 8 you make 4 and 4, and do not land on ten.
First work out what 7 needs to make ten: 3. Split the 8 into 3 and the rest.
You forget the ten: for 7 + 8 you say 5.
You crossed ten, so the answer is more than 10.
Tips
- Start at the bigger number and make that up to 10.
- What is left over is always small, so the second step is easy.
Why it works
Counting up to ten is easy, and so is counting on from ten: 10 + 5 is just 15. The hard part is crossing ten. If you split the second number, one hard step becomes two easy ones.