Add & Subtract Within 100

26 = 20 + 6.

8.

I know there are 4 tens + 5 tens. 4 + 5 = 9. There are 9 tens in all. 40 + 50 = 90.

I know there are 6 tens to start. I can take away 4 tens from 6 tens. 6 – 4 = 2. There are 2 tens, or 20, left. 60 – 40 = 20.

18 = 1 ten and 8 ones.

I can break apart numbers by their place values, and then add the separate place values together. For example, 82 = 80 + 2. 17 = 10 + 7. 80 + 10 = 90. 2 + 7 = 9. The final sum is 90 + 9 = 99.

I need to regroup if I add the ones and the number is 10 or greater. I regroup 10 ones as 1 ten.

26 + 12 = 38. 20 + 10 = 30. 6 + 2 = 8. There are only 8 ones, so I don’t need to regroup.

I need to regroup if the number of ones I need to subtract is greater than the number of ones I'm subtracting from. I regroup 1 ten from the first number as 10 ones. For example, 34 – 29. I regroup 1 ten from 34 as 10 ones. So 34 = 20 + 14. Then I subtract the ones and the remaining tens.

34 is 3 tens and 4 ones. 29 is 2 tens and 9 ones. 9 ones are more than 4 ones, so I need to regroup. 34 = 20 + 14. Subtract the ones. 14 – 9 = 5. Subtract the tens. 20 – 20 = 0. The answer is 5.