0:00:00.445,0:00:05.006 We're told that Linde isn't sure[br]how to subtract 853... 0:00:07.216,0:00:09.826 We are told Linde isn't sure 0:00:09.826,0:00:14.001 how to subtract 853 minus 283. 0:00:14.265,0:00:16.644 Help Linde by choosing an expression 0:00:16.644,0:00:21.444 that is the same as 853 minus 283. 0:00:21.532,0:00:24.464 So, pause this video and see[br]if you can answer it on your own 0:00:24.514,0:00:26.719 before we work through it together. 0:00:26.797,0:00:29.297 Alright, now that we look[br]at all the choices, 0:00:29.297,0:00:31.321 they all start with 853. 0:00:31.361,0:00:34.722 Now, this first choice[br]they subtract out 200 0:00:34.776,0:00:37.006 That makes sense[br]because we have 2 hundreds 0:00:37.006,0:00:38.515 right over there. 0:00:38.653,0:00:40.734 Then they subtract out 50 0:00:40.754,0:00:43.036 and then they subtract out 3, 0:00:43.446,0:00:46.046 So, the 200 and the 3 make sense. 0:00:46.146,0:00:49.206 You can view 853 minus 283 0:00:49.286,0:00:54.050 as 853 minus 200, 0:00:55.205,0:00:57.910 minus 80, 8 tens right here, 0:00:57.930,0:00:59.185 minus 3. 0:00:59.185,0:01:01.216 But that's not what they wrote over here. 0:01:01.236,0:01:03.276 Instead of putting 80 here,[br]they put a 50. 0:01:03.326,0:01:04.626 So we can rule that out. 0:01:04.655,0:01:06.608 Here we have 853 minus 20 0:01:06.648,0:01:08.722 minus 800 minus 3. 0:01:08.772,0:01:11.032 Well, this is a little bit strange 0:01:11.062,0:01:13.664 because we don't have 2 tens,[br]we have 2 hundreds 0:01:13.664,0:01:16.704 and we don't have 8 hundreds,[br]we have 8 tens, 0:01:16.744,0:01:18.712 so this is also incorrect. 0:01:18.872,0:01:20.892 Now, it's probably going to be this one, 0:01:20.912,0:01:23.629 but let's just make sure[br]we feel comfortable with this. 0:01:23.669,0:01:26.599 So, this one has 853 minus 200, 0:01:26.674,0:01:28.615 minus 53. 0:01:28.685,0:01:30.601 minus 30. 0:01:30.921,0:01:33.377 Does that make sense? 0:01:33.407,0:01:34.952 Well, let's think about it. 0:01:35.040,0:01:36.297 What they're doing, 0:01:36.297,0:01:38.639 is they're subtracting out first the 200, 0:01:38.639,0:01:41.288 so that this part right over here,[br]so that makes sense. 0:01:41.308,0:01:43.141 They're subtracting out first that. 0:01:43.273,0:01:45.161 And then they're subtracting out 53 0:01:45.201,0:01:47.029 and then subtracting out 30. 0:01:47.029,0:01:48.777 Well, that is the same thing 0:01:48.777,0:01:50.627 as subtracting out 83, 0:01:50.627,0:01:52.344 because subtracting out 83 0:01:52.344,0:01:54.414 is the same thing[br]as subtracting out 53 and 0:01:54.414,0:01:56.181 and then subtracting 30. 0:01:56.209,0:01:57.436 53 plus 30 is 83. 0:01:57.449,0:01:58.847 Now, you might be wondering 0:01:58.847,0:02:00.557 why would they even do it this way? 0:02:00.587,0:02:02.716 What is easier to do in your head? 0:02:02.777,0:02:06.727 853 minus 200 is 653. 0:02:07.125,0:02:09.628 You take away 53 from that, 0:02:10.168,0:02:12.301 so you take away 53 from that, 0:02:12.301,0:02:14.563 and you're going to be left with 600. 0:02:15.013,0:02:17.150 And then 600 minus 30 0:02:17.150,0:02:19.148 — you might recognize that, 0:02:19.148,0:02:21.829 you could do 60 tens minus 3 tens — 0:02:22.183,0:02:23.543 it's going to be 57 tens, 0:02:23.593,0:02:25.613 or you might be able[br]to do it in your head 0:02:25.623,0:02:28.474 600 minus 30 is 570. 0:02:28.536,0:02:30.366 So, that's why they broke out, 0:02:30.366,0:02:31.892 they broke up the 83. 0:02:31.942,0:02:34.103 Instead of just breaking it up[br]into 80 and 3, 0:02:34.117,0:02:38.487 they broke it up into 53 and 30[br]to match this 53 over here. 0:02:38.687,0:02:41.147 It's easier to work out the result. 0:02:41.427,0:02:42.692 Let's do another example. 0:02:42.712,0:02:45.257 So, here we're asked to fill in the blank. 0:02:45.267,0:02:50.276 They say, 143 minus 79[br]is the same as "blank" minus 80. 0:02:50.367,0:02:53.227 So, pause this video[br]and see if you can figure this out. 0:02:53.477,0:02:55.697 So, the key here is to realize 0:02:55.717,0:02:57.526 is, when you have a difference here, 0:02:57.526,0:02:59.849 as long as you add or subtract[br]the same amount 0:02:59.889,0:03:01.169 to both of these, 0:03:01.189,0:03:03.179 the difference will be the same. 0:03:03.189,0:03:06.287 So, it looks like they tried[br]to turn 79 into, 0:03:06.377,0:03:10.239 it looks like they turned[br]the 79 into an 80, 0:03:10.339,0:03:12.174 by adding 1 0:03:12.204,0:03:14.495 and so if we want the difference[br]to be the same, 0:03:14.515,0:03:17.976 we would add 1 to the 143 as well, 0:03:18.296,0:03:21.556 So, 143 plus 1 is 144. 0:03:21.586,0:03:23.703 If we add one to both of these numbers, 0:03:23.743,0:03:25.883 the difference would be the same. 0:03:25.920,0:03:27.320 And we're done. 0:03:27.450,0:03:29.490 So it's 144 minus 80.