Subtraction to 20!

We are learning about subtraction.
If we are subtracting 3 from 17 (17-3) we can subtract from the ones.
See how good we are!

17-3=

14!

18-3=

15!

     Sometimes we don't have enough ones to take away from the ones. If our subtraction problem is 12-7 we can't take 7 from the 2 so we have to take 7 from the 10.

10-7 = 3 then we need to add the 3 to the 2 to get 5
So.....12-7=5

These strategies will get us ready for subtraction with regrouping! However, we also need to practice our math facts because that will make double digit subtraction much easier!

OA.C.6

Operations & Algebraic Thinking
Add and subtract within 20.

6. Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Addition and subtraction (This may or may not be helpful...feel free to decide for yourself. She is demonstrating the strategies we use in class.)

I'll leave you with this joke:
Q: Why didn’t the quarter roll down the hill with the nickel?
A: Because it had more cents.