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## Strategies for adding and subtracting within 100

Current time:0:00Total duration:2:50

## Video transcript

- [Voiceover] What I wanna show you now is a way to add numbers, or a way that I sometimes add numbers, when I'm doing it in my head. So let's say I wanna add five to 68. And we've already seen
other ways of doing it, so what I'm showing in this video isn't the only way to do it but it might be helpful when
you're doing it in your head. Well when I look at a number
like 68 I think well gee, If I added just two to
that I would get to 70. So why don't I break up
five into three and two, add the two to 68 and then
I have to add the three. So what's that going to get me? Well if I break up the
five into three plus two, and the whole reason why I
broke it up into three and two is so I have this two here to add to 68. So five is three plus two, and to that I'm going to add 68, 68. And once again the reason
why I took this two out is because I said hey, what do I have to add to 68 to get to 70? So now I could just rewrite this as, Three plus two plus 68, 68. But now I can add the two to the 68. So two plus 68 is going to be Two plus 68 is 70. 70 and I still have this three here, so I have three plus 70
which is equal to 73. 73. Now it might seem like this
really long way of doing it, but this is just a way to think about it. In your head you'd say okay five plus 68, let's see if I add two
to 68 I'll get to 70 and so let's see, five is three plus two, I add the two to 68, I get to 70, and I have three left over. So it's going to be 73. Another way you could think
about it is on a number line. So let's draw ourselves
a number line here. Let's draw a number line
and let me draw some let me draw some tick marks here. And let's say that this right over here, this right over here is 68, and so this is going to be 70, this is going to be 70, and we're gonna add five. We're gonna add five. So if you add five you say
well let me add two first. So if I add two first I get to 70. So plus two, that's what I did right
over here to get to 70, and then if I wanna add five
then I have to add three more. Then I have to add three more. And so it's going to be 70 plus three. Which of course is 73. Hopefully you found that interesting.