Addition bridging tens
You learn to add and subtract across a ten by jumping to the ten first.
How to work it out
- Split the second number so you land on a multiple of ten.
- Jump to that ten first.
- Then add or subtract the rest.
A worked example
76 + 8
- Split 8 into 4 and 4, because 76 + 4 = 80.
- Jump to 80.
- Then jump on with the rest: 80 + 4 = 84.
More examples
56 − 8
- Split 8 into 6 and 2, because 56 − 6 = 50.
- Jump back to 50.
- Then jump back with the rest: 50 − 2 = 48.
47 + 5
- Split 5 into 3 and 2, because 47 + 3 = 50.
- Jump to 50.
- Then jump on with the rest: 50 + 2 = 52.
Try it yourself
53 + 9 =
72 + 9 =
Watch out
You forget that you cross the ten: for 76 + 8 you say 74.
You go past 80, so the tens go up by one: the answer starts with an 8.
For 56 − 8 you do 8 − 6 = 2 and say 52.
You cannot take 8 from 6. Jump back to 50 first, then take away the rest.
Tips
- Split the second number so that you land exactly on the ten.
- Draw the jumps on a number line if you cannot see it.
Exceptions
- If you do not cross the ten, like 71 + 5, you do not need to split: just add the ones.
Why it works
For 76 + 8 you go past 80. If you jump to 80 first, one hard step becomes two easy ones: 76 + 4 and 80 + 4. Subtracting works the same way, but then you jump back to the ten.