Subtraction

My students know... when we do subtraction, we THINK ADDITION!

There are many ways to do subtraction but these are the ways I've taught.

First there is counting up. This is when the "making ten" strategy comes into play.

So here we got 38 up to a friendly number 40 by adding 2, then we went from 40 to our original number by adding 23. Then we add those two numbers together. 2 plus 23 is 25. So I needed 25 to get from 38 to 63. 

25 is my answer.

Here is Leon demonstrating how to get from 29 to 56. First you add 1 to get to the friendly number 30, then you add another 26 to get to our original number. Then you add 1 and 26 together and get 27. I needed 27 to get from 29 to 56. 

This is the same problem as above. 63-38.

I started by drawing 6 ten rods and 3 ones. Then I couldn't take 8 away from 3 so I had to change from a ten rods to 10 ones. (I usually draw it over the line so the kids realize I'm not adding any numbers, just changing the format). Then I can cross out my 8 ones, and I cross out my 3 tens.

Then I count what is left. 2 ten rods and 5 ones.

We do NOT teach the "borrowing" way yet.
This is because it can interfere with understand the number sense and place value. Eventually when I do teach it, hopefully  absolutely they will understand it because we've drawn the ten rods and make it into 10 ones.

Thank you to Rachael's family for asking me about subtraction. I can't believe I hadn't put it on the blog yet. My apologies!