Addition with carrying
By the end of this lesson a child adds two numbers whose sum is greater than 10. Ones that pass ten become one ten. That step is called carrying.
What the child can do at the end
- For 8 + 5, first fill 8 up to 10, then add what is left.
- Know that 8 + 2 = 10, and 3 remain from the 5, so the sum is 13.
- Does not write 13 as only 3, with the ten left out.
Why the sum crosses 10
Ten ones are one ten. When there are more than 9 ones, a full ten is set aside and the rest stays as ones. So 8 + 5 is not 13 by memory. It is 10 and 3 more.
One problem, step by step
Ana has 8 marbles. She gets 5 more. How many marbles does she have now?
- From the 5 marbles, take 2, because 8 + 2 fills a ten.
- 8 + 2 = 10. That is one full ten.
- 2 of the 5 are used, so 3 marbles remain.
- 10 + 3 = 13. Ana has 13 marbles: one ten and 3 ones.
A common mistake
The child adds 8 + 5 and writes 3, because they see only what is left after ten. The ten is not lost. The answer has two digits: 1 for the ten and 3 for the ones, so 13.
The other mistake is 8 + 5 = 12. The child fills up to 10, then adds 2 instead of 3. Of the 5, two make the ten, and 3 remain, not 2.
Practice
- 7 + 4 = ___
- 9 + 3 = ___
- 6 + 6 = ___
- 8 + 6 = ___
- 5 + 8 = ___
In words: 9 sweets and 2 more. How many in all?
Answers
- 11 — 3 are needed to make 10, and 1 remains
- 12 — 1 is needed to make 10, and 2 remain
- 12
- 14
- 13
Sweets: 9 + 1 = 10, plus 1 more, which is 11.
After the lesson, the quiz
Open the addition quiz and the table. If the sum passes 10 and the child writes one digit, go back to the step “fill the ten first”.
For a parent
Put 10 spaces in an egg carton. When the carton is full, the extra pieces sit beside it. The carton is the ten, and the extra pieces are the ones.