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We're asked to subtract.[br]And we have the problem 68 - 42.

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And what I want to do here, is [br]1) just show you how I would do this problem,

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and then, talk a little bit [br]about why it actually works.

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So if I have 68 - 42, one way to do it – [br]and this is probably the most typical way –

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is to write the number you're[br]subtracting from on top,

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and to write the number that you're [br]subtracting from that number below that.

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So we're going to have 68 - 42.

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And the thing you really want to think[br]about – or to make sure you do,

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is to align your numbers according to place.

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So the 2 is below the 8 –[br](They're both in the 1's place.)

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– and the 4 is below the 6.[br](They're both in the 10's place.)

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And later in this video it should be [br]clear – or I'll hopefully make it clear –

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why that's a good thing to do.

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Alright. So then we go to [br]the 1's place, and we see an 8.

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And from that, we're[br]going to subtract a 2.[br]

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So, 8 - 2 is 6. (8 - 2 = 6)[br]I'll write that over here.

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Let me write that over here.

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8-2 is 6.

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8 - 2 is equal to 6. [br](Repeating: 8 - 2 = 6)

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And then we go to the 10's place.[br]We have 6 - 4.

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And since they're in the 10's place, [br]this is really 60 - 40.

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But 6 - 4 is 2.[br]6 - 4 = 2.

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And since these are in the 10's place, [br]this is really saying 60 - 40 = 20.

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And I'll make that a little bit clearer in a second.

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So we're actually done here.

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68 - 42 = 26.

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And you can check that for yourself.

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If you add 26 + 42,[br]you should get 68.

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Or if you subtract 26 from 68[br]you should get 42.

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So I encourage you do that in [br]your own time after this video –

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verify that 42 + 26 = 68.

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And also verify what 68 - 26 is equal to.

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And you should see that is equal to 42.

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So these are two things for [br]you to check on your own.

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Now, the last thing I want to do[br]in this video is just to explain

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in a little bit more depth why this actually works.

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And, at least in my mind, I like to visualize 68 –

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(You won't to have write it out like this –

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but it's one way to make sure you[br]really understand what is going on here.)

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68 is the same thing as 60 + 8, or 60 and 8.

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And from that, we're subtracting 42.

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But 42 is the same thing as 40 + 2.

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So we're subtracting 40,[br]and we're subtracting 2.

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We're subtracting 42.[br]We're subtracting 40 and 2.

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And so you can view this as [br]really two separate problems.

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You have, in the 1's place, you have 8 - 2.

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And that is exactly what we did over here.[br]You have a 6.

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And then in 10's place,[br]you have 60 - 40, which is 20.

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So you end up with 20 + 6.

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and you know that that is [br]the same exact thing as 26.