WEBVTT 00:00:00.358 --> 00:00:04.893 We're asked to subtract. And we have the problem 68 - 42. 00:00:04.893 --> 00:00:09.140 And what I want to do here, is 1) just show you how I would do this problem, 00:00:09.140 --> 00:00:12.516 and then, talk a little bit about why it actually works. 00:00:12.516 --> 00:00:17.533 So if I have 68 - 42, one way to do it – and this is probably the most typical way – 00:00:17.533 --> 00:00:20.759 is to write the number you're subtracting from on top, 00:00:20.759 --> 00:00:24.507 and to write the number that you're subtracting from that number below that. 00:00:24.507 --> 00:00:27.122 So we're going to have 68 - 42. 00:00:27.122 --> 00:00:30.200 And the thing you really want to think about – or to make sure you do, 00:00:30.200 --> 00:00:32.277 is to align your numbers according to place. 00:00:32.277 --> 00:00:35.501 So the 2 is below the 8 – (They're both in the 1's place.) 00:00:35.501 --> 00:00:38.732 – and the 4 is below the 6. (They're both in the 10's place.) 00:00:38.732 --> 00:00:41.585 And later in this video it should be clear – or I'll hopefully make it clear – 00:00:41.585 --> 00:00:44.144 why that's a good thing to do. 00:00:44.144 --> 00:00:47.397 Alright. So then we go to the 1's place, and we see an 8. 00:00:47.397 --> 00:00:49.738 And from that, we're going to subtract a 2. 00:00:49.738 --> 00:00:53.533 So, 8 - 2 is 6. (8 - 2 = 6) I'll write that over here. 00:00:53.533 --> 00:00:54.790 Let me write that over here. 00:00:54.790 --> 00:00:56.359 8-2 is 6. 00:00:56.359 --> 00:01:02.200 8 - 2 is equal to 6. (Repeating: 8 - 2 = 6) 00:01:02.200 --> 00:01:05.604 And then we go to the 10's place. We have 6 - 4. 00:01:05.604 --> 00:01:08.667 And since they're in the 10's place, this is really 60 - 40. 00:01:08.667 --> 00:01:15.604 But 6 - 4 is 2. 6 - 4 = 2. 00:01:15.604 --> 00:01:19.686 And since these are in the 10's place, this is really saying 60 - 40 = 20. 00:01:19.722 --> 00:01:21.850 And I'll make that a little bit clearer in a second. 00:01:21.850 --> 00:01:22.815 So we're actually done here. 00:01:22.815 --> 00:01:26.261 68 - 42 = 26. NOTE Paragraph 00:01:26.261 --> 00:01:28.143 And you can check that for yourself. 00:01:28.143 --> 00:01:31.466 If you add 26 + 42, you should get 68. 00:01:31.466 --> 00:01:35.959 Or if you subtract 26 from 68 you should get 42. 00:01:35.959 --> 00:01:39.005 So I encourage you do that in your own time after this video – 00:01:39.005 --> 00:01:46.178 verify that 42 + 26 = 68. 00:01:46.178 --> 00:01:50.867 And also verify what 68 - 26 is equal to. 00:01:50.867 --> 00:01:52.697 And you should see that is equal to 42. 00:01:52.697 --> 00:01:56.100 So these are two things for you to check on your own. 00:01:56.100 --> 00:01:59.133 Now, the last thing I want to do in this video is just to explain 00:01:59.133 --> 00:02:01.667 in a little bit more depth why this actually works. 00:02:01.667 --> 00:02:05.400 And, at least in my mind, I like to visualize 68 – 00:02:05.400 --> 00:02:07.025 (You won't to have write it out like this – 00:02:07.025 --> 00:02:09.348 but it's one way to make sure you really understand what is going on here.) 00:02:09.348 --> 00:02:15.324 68 is the same thing as 60 + 8, or 60 and 8. 00:02:15.324 --> 00:02:17.723 And from that, we're subtracting 42. 00:02:17.723 --> 00:02:21.348 But 42 is the same thing as 40 + 2. 00:02:21.364 --> 00:02:25.769 So we're subtracting 40, and we're subtracting 2. 00:02:25.769 --> 00:02:29.200 We're subtracting 42. We're subtracting 40 and 2. 00:02:29.200 --> 00:02:32.194 And so you can view this as really two separate problems. 00:02:32.194 --> 00:02:35.415 You have, in the 1's place, you have 8 - 2. 00:02:35.415 --> 00:02:38.200 And that is exactly what we did over here. You have a 6. 00:02:38.200 --> 00:02:44.267 And then in 10's place, you have 60 - 40, which is 20. 00:02:44.267 --> 00:02:46.867 So you end up with 20 + 6. 00:02:46.867 --> 00:02:53.105 and you know that that is the same exact thing as 26.