1 00:00:00,651 --> 00:00:05,201 We're asked to subtract, we have the problem 68-42. 2 00:00:05,201 --> 00:00:08,940 And what I wanna do here, is one just show you how I would do this problem 3 00:00:08,940 --> 00:00:12,516 and then talk a little bit about why it actually works 4 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 5 00:00:17,533 --> 00:00:20,759 is to write the number you're subtracting from on top, 6 00:00:20,759 --> 00:00:24,507 and to write the number that you're subtracting from that number below that 7 00:00:24,507 --> 00:00:27,353 So we're going to have 68-42. 8 00:00:27,353 --> 00:00:30,200 And the thing you really want to think about, or to make sure you do, 9 00:00:30,200 --> 00:00:34,077 is it you want to align it according to place, so the 2 is below the 8 10 00:00:34,077 --> 00:00:37,133 they're both in the one's place, and the 4 is below the 6, 11 00:00:37,133 --> 00:00:40,533 they're both in the ten's place. And later in this video it should be clear, 12 00:00:40,533 --> 00:00:43,800 or I'll hopefully make it clear why that is a good thing to do. 13 00:00:43,800 --> 00:00:46,138 Alright, so then we go to the one's place, 14 00:00:46,138 --> 00:00:52,431 and we see an 8, and from that we're going to subtract a 2, so, 8-2 is 6. 15 00:00:52,431 --> 00:00:53,533 Write that over here. 16 00:00:53,533 --> 00:00:55,067 Write that over here. 17 00:00:55,067 --> 00:00:56,667 8-2 is 6. 18 00:00:56,667 --> 00:01:02,200 8-2=6. 19 00:01:02,200 --> 00:01:05,759 And then we go to the ten's place, we have 6-4. 20 00:01:05,759 --> 00:01:08,667 And since they're in the the ten‘s place, this is really 60-40. 21 00:01:08,667 --> 00:01:15,604 But 6-4 is 2, 6-4=2. 22 00:01:15,604 --> 00:01:18,810 and since these are in the ten’s place, this is really saying 60-40. 23 00:01:18,810 --> 00:01:20,015 is equal to 20. 24 00:01:20,015 --> 00:01:21,850 I will make that a little bit clearer in a second. 25 00:01:21,850 --> 00:01:23,015 So actually we done here. 26 00:01:23,015 --> 00:01:26,600 68-42=26 27 00:01:26,600 --> 00:01:28,143 and you can check that for yourself 28 00:01:28,143 --> 00:01:31,267 if you add 26 plus 42 you should get 68 29 00:01:31,267 --> 00:01:35,667 or if you subtract 26 from 68 you should get 42. 30 00:01:35,667 --> 00:01:39,267 So I encourage you do that in your own time after this video 31 00:01:39,267 --> 00:01:44,533 verify that 42+26=68 32 00:01:44,533 --> 00:01:46,533 is equal to 68 33 00:01:46,533 --> 00:01:50,867 and also verify what 68-26 is equal to 34 00:01:50,867 --> 00:01:52,867 and you should see that is equal to 42 35 00:01:52,867 --> 00:01:56,100 so these are two things for you to check on your own 36 00:01:56,100 --> 00:01:59,133 Now, the last thing I want to do in this video is just explain 37 00:01:59,133 --> 00:02:01,667 in a little bit more depth why this actually works 38 00:02:01,667 --> 00:02:05,400 and at least in my mind I like to visualize 68 39 00:02:05,400 --> 00:02:07,133 you won't to have write it out like this 40 00:02:07,133 --> 00:02:09,610 but it is one way to make sure you really understand what is going on here 41 00:02:09,610 --> 00:02:15,324 68 is the same thing as 60 plus 8 or 60 and 8 42 00:02:15,324 --> 00:02:17,723 and from that we're subtracting 42 43 00:02:17,723 --> 00:02:21,348 but 42 is the same thing as 40 plus 2 44 00:02:21,364 --> 00:02:26,000 so we are subtracting 40 and we are subtracting 2 45 00:02:26,000 --> 00:02:29,200 we are subtracting 42, we are subtracting 40 and 2. 46 00:02:29,200 --> 00:02:32,410 and so you can view this as really two separate problems 47 00:02:32,410 --> 00:02:35,415 you have in the one’s place, you have 8-2 48 00:02:35,415 --> 00:02:38,200 and that is exactly what we did over here, you have the 6 49 00:02:38,200 --> 00:02:44,267 and then in ten‘s place you have 60-40, which is 20 50 00:02:44,267 --> 00:02:46,867 so you end up with 20+6 51 00:02:46,867 --> 00:02:53,105 and you know that that is the same exact thing as 26.