Tom Schersten: We’re going to model addition on a number line. I’m adding the same two numbers I did in the previous video, 35 add 27, and on my number line, I’ve placed my 35 and my 27.

To start this problem, I’m going to make my dot here, and write down that I’m starting with 35. It’s my choice what part of the 27 I add next, and I think what I would like to do is add this 20, so I’m going to draw a line that says I’m adding 20. When I have everything put together, I see that what I have is now a total of 55.

The next thing I’d like to do is to then add the 7, and when we put our 7 in there, what we have is 10, 20, 30, 40, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62. I’m now going to model adding 35 and 27 a different way on a number line.

Again, I’m starting with my 35. I’m making a dot on my number line, and writing down the 35 I’m starting with. This time what I would like to add is just 5, because if I take 5 ones from my 7, and put them with the 5 ones from the 35, I have enough ones to trade for another 10. I’m going to do that trade, and then after adding that 5 I see that what I have is a total of 40.

The next thing I think I would like to add is the 2, and when I add the 2 to my total I have a total of 42. Now I’m going to add in the extra 20, and when I add that 20, I see that my total is 62. This simply shows what I’m adding, and in which order.

I have the addends here, and the cumulative totals. The next video is going to show how to do subtraction on a number line.