Mental Math Tricks - Addition and Subtraction in your head! - By tecmath
Transcript
| 00:00 | Good day and welcome to the Tech Math channel . | |
| 00:02 | In this video I'm going to be having a look | |
| 00:04 | at is how to mentally added some tract larger numbers | |
| 00:08 | . I'm going to deal with two digit numbers for | |
| 00:09 | the minute . Uh , okay . But these are | |
| 00:12 | gonna be looking at how to add and subtract these | |
| 00:14 | in your head . Now look , some people straight | |
| 00:15 | away . I think this is good . Nisi . | |
| 00:17 | I know how to do this already . And look | |
| 00:19 | personally , I've always found this a little bit easier | |
| 00:21 | , but I'll show you the way that I tend | |
| 00:24 | to work this out because it's not something that comes | |
| 00:26 | naturally to everybody . Okay . Uh , and if | |
| 00:29 | it doesn't , don't worry , I'm gonna show you | |
| 00:31 | how , how we do it . Okay , so | |
| 00:34 | this is a really good skill , which you can | |
| 00:35 | do either . You will be able to do easily | |
| 00:37 | . So start with an example here . What about | |
| 00:40 | something like , uh , what about I say there's | |
| 00:42 | 43 plus 17 . Do you get 60 straight away | |
| 00:47 | ? Well , I'll show you the way that I | |
| 00:49 | work these out . 43 Plus 17 . Okay . | |
| 00:54 | The way that I think about this is as follows | |
| 00:57 | , I actually my mind orders it like this , | |
| 01:01 | and probably a few people might have a few comments | |
| 01:03 | on this , and I'll be interested to see how | |
| 01:05 | people's minds differ when they do this . My mind | |
| 01:08 | , what it would do Would do this , I | |
| 01:10 | would go 43 plus seven , which would equal 50 | |
| 01:20 | . And then what I would do is I would | |
| 01:21 | add , so that's the seven there I've added , | |
| 01:23 | and then I would add the 10 plus 10 equals | |
| 01:27 | 60 . Okay , And that's how I mentally add | |
| 01:33 | things . Okay ? Uh look sometimes you might decide | |
| 01:36 | that you're going to add the 11th or you're going | |
| 01:38 | to add the seven first , It doesn't really matter | |
| 01:40 | . Uh Typically it's a lot easier to add the | |
| 01:43 | smaller numbers on rather than going 17 plus 43 . | |
| 01:45 | But again , that doesn't really matter either . But | |
| 01:47 | you could have quite as easily gone . 43 plus | |
| 01:49 | 10 is 53 plus seven is 60 . Okay . | |
| 01:54 | You see what I mean with that ? So it's | |
| 01:56 | a really , really easy trick . Okay . And | |
| 01:59 | some people are going to go , hey , that's | |
| 02:00 | not a trick at all . And look in some | |
| 02:02 | ways for some people , this is something that instinctively | |
| 02:05 | comes to them . Okay . But there's a degree | |
| 02:07 | of people that won't . So this is the people | |
| 02:10 | this video is for Okay , What about something like | |
| 02:14 | 37 plus 68 . Okay . 37 plus 68 . | |
| 02:21 | Hopefully you get the answer of 100 and five . | |
| 02:26 | So 37 plus 68 . So you remember how I | |
| 02:33 | did this , what this accord as I go first | |
| 02:37 | off , I'm adding the 60 here Or I can | |
| 02:41 | have the eight but I'm going to add the 60 | |
| 02:43 | on this one . So 37 plus 60 is 97 | |
| 02:48 | plus . I'd 97 plus eight is 100 and five | |
| 02:54 | . Okay . But I could have just as easily | |
| 02:56 | done it the other way and I could do on | |
| 02:57 | 37 plus eight is 45 and then I 45 plus | |
| 03:03 | 60 is 100 and five . Okay . It doesn't | |
| 03:07 | really matter which way you do it with that . | |
| 03:09 | Okay , so this is the way that when you | |
| 03:11 | see people adding and they're really really proficient at it | |
| 03:15 | . This is how we can do it . Okay | |
| 03:17 | . It's a matter of first jumping with the units | |
| 03:19 | or the tens and then jumping with the other one | |
| 03:21 | . Okay . So hopefully you go with this . | |
| 03:23 | What about we try subtraction here ? All right . | |
| 03:29 | Ah what about say 80 to take away 14 . | |
| 03:33 | I'll write that down while you work it out 80 | |
| 03:36 | to take away 14 . So what answer did you | |
| 03:41 | get for that ? So 82 take away four . | |
| 03:45 | So 82 take away for equals 78 And then 78 | |
| 03:54 | Take away the 10 equals 68 . Okay , so | |
| 04:00 | you do have to do those little steps in it | |
| 04:02 | . Okay ? You have to account for everything with | |
| 04:04 | those . So 80 to take away 1468 . Yeah | |
| 04:09 | . So we're going Down by 4-78 , then down | |
| 04:12 | by 10 to 68 . No problem . Okay . | |
| 04:19 | What about I give you another example here . uh | |
| 04:22 | what about this one ? What about we do uh | |
| 04:25 | 55 Take away 39 to take away the 9 1st | |
| 04:33 | and you could get the answer of Uh huh . | |
| 04:36 | 46 take away the 30 We end up with 16 | |
| 04:42 | . Okay , So this one 55 take away the | |
| 04:47 | nine take away nine vehicles , 46 . And then | |
| 04:56 | from the 46 we go down three steps . 30 | |
| 05:02 | steps and we get 16 . How do you find | |
| 05:08 | them ? No problem . We'll tell you what what | |
| 05:13 | I'll do is I'll put a couple of examples up | |
| 05:15 | here and we'll see how you can go with them | |
| 05:17 | . Okay , What about uh jot a number of | |
| 05:21 | them ? Some additions of subtraction ones , and we'll | |
| 05:23 | see how you go . You might pause them and | |
| 05:25 | then see how you go . All right , So | |
| 05:30 | what about uh 72 take away 24 , 33 plus | |
| 05:40 | 29 And Uh huh . We'll do 100 yet actually | |
| 05:48 | , why not ? 105 plus 77 . Okay . | |
| 05:56 | See here you go with those . All right , | |
| 05:59 | so first off 72 we're going to add we're gonna | |
| 06:03 | we're taking away . I've been not start adding well | |
| 06:05 | , it's a bit of a trick there , isn't | |
| 06:07 | it ? Better pay attention to the actual sign , | |
| 06:09 | 70 to take four is 68 . Take 20 is | |
| 06:16 | 48 . Okay . How did you go with that | |
| 06:20 | ? Hopefully good . 33 plus nine is 42 plus | |
| 06:26 | 20 is 62 . 105 plus seven Is 112 plus | |
| 06:35 | 70 is 100 and 82 . They're not too bad | |
| 06:42 | , are they ? Hopefully you do pretty good with | |
| 06:44 | those practices a lot . Some people again are going | |
| 06:47 | to be fine at those already and they're probably tuned | |
| 06:49 | out already . But if you're just starting with those | |
| 06:52 | good luck on those , it's a really , really | |
| 06:54 | great skill and the more you do that , this | |
| 06:56 | is one of these basic maths things , which is | |
| 06:59 | probably the most important thing you get . And that's | |
| 07:00 | why I'm making this video . Okay , So keep | |
| 07:03 | practicing it and hopefully you get really good at it | |
| 07:06 | . I'll see you next time . |
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Mental Math Tricks - Addition and Subtraction in your head! is a free educational video by tecmath.
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