Fractions subtraction trick - the fast way! - By tecmath
Transcript
| 00:01 | Good day . Welcome to take Math Channel . What | |
| 00:03 | we're going to be having a look at this video | |
| 00:04 | is we're going to be looking at how to subtract | |
| 00:07 | one fraction from another . This is a fairly simple | |
| 00:09 | sort of our thing to do using this thing called | |
| 00:12 | the Bowtie methods . So Let's have a look at | |
| 00:14 | this to say you were asked to get 3/4 and | |
| 00:18 | take away 2/3 . This is gonna be much like | |
| 00:23 | adding fractions . We've looked at these in another video | |
| 00:25 | , but if you haven't seen this or or maybe | |
| 00:28 | you just might want to know the minor differences . | |
| 00:30 | These continue watching . So first off , how are | |
| 00:33 | we going to do this ? First off , you | |
| 00:35 | might realize that when we are subtracting or adding of | |
| 00:38 | one fraction to another or from another , we have | |
| 00:41 | to have these bottom numbers , these denominators the same | |
| 00:44 | . Okay , so the easiest way to do that | |
| 00:47 | is to multiply them together . Okay , so if | |
| 00:50 | we could do that four times three Is 12 and | |
| 00:53 | because this is going to be the same denominator years | |
| 00:56 | , I'm just going to put everything over the top | |
| 00:58 | of this denominator now rather than writing a separate one | |
| 01:00 | for each . So what number did we times this | |
| 01:04 | ? four by to get 12 ? Were times that | |
| 01:07 | by three . Okay , so we have two times | |
| 01:10 | this number up here , also by three to keep | |
| 01:12 | this fraction equivalent . Okay , this one's times in | |
| 01:15 | by three . So this one times by three . | |
| 01:18 | This number is timing by this number . Okay . | |
| 01:21 | Three threes adored . What number do we times is | |
| 01:26 | three by to get 12 . 4 times to buy | |
| 01:28 | this number here . Before . So we're also going | |
| 01:30 | after Times is two by 42 fours eight . And | |
| 01:35 | we keep the symbol in the middle of the same | |
| 01:37 | . It's just really important when you do this , | |
| 01:39 | make sure you start with the left hand ones first | |
| 01:42 | and then go to the right hand fractions . Okay | |
| 01:44 | , don't mix those up or you will get the | |
| 01:45 | wrong answer . So nine take away eight is one | |
| 01:50 | , and the bottom number stays the same , and | |
| 01:53 | that's how we solve these . Okay , so we | |
| 01:55 | multiply these two numbers first from left to bottom , | |
| 01:59 | right from right to bottom left . Okay , we're | |
| 02:03 | multiplying and then we just carried out using that symbol | |
| 02:06 | there and it's as simple as that . Okay , | |
| 02:08 | so what about we have a look at another one | |
| 02:11 | of these . What about we have a look at | |
| 02:15 | say uh let's get uh 4/5 and we'll take away | |
| 02:20 | a half . I'm going to go fairly simple ones | |
| 02:22 | . I don't want to start getting silly numbers and | |
| 02:24 | that's not that they can't be done . It's just | |
| 02:26 | they get a bit annoying to deal with you . | |
| 02:28 | So we're going to use that same sort of method | |
| 02:30 | here . Let's go . Red pen now . Okay | |
| 02:34 | , let's get this bottom number multiply these five times | |
| 02:37 | two is 10 . Okay , What are we gonna | |
| 02:42 | do now ? Okay , So we multiplied five times | |
| 02:45 | too . So we're going to multiply four times to | |
| 02:46 | Okay , so four times two is eight and now | |
| 02:51 | we're going to have to do is multiply this one | |
| 02:54 | times five . Okay . One times five is five | |
| 02:59 | . And we keep the suit the symbol in the | |
| 03:00 | same in the middle of the same subtract . Okay | |
| 03:04 | , So eight take away five is three , answer | |
| 03:07 | is 3/10 . Okay . All right . Um Now | |
| 03:14 | let's just go one more of these to say what | |
| 03:19 | we were doing . Is I was asking you to | |
| 03:21 | get uh what about four 7th ? And I'm going | |
| 03:29 | to take away what else ? Okay . Alright . | |
| 03:35 | You give this a go and see . Here you | |
| 03:36 | go . All right . You're giving it a go | |
| 03:38 | already . I'm pretty sure you pause the video . | |
| 03:39 | Otherwise you should , but I'm going to answer this | |
| 03:41 | right now . So 7-14 . Big Lawn . Okay | |
| 03:47 | . So that was those ones four twos I 17 | |
| 03:53 | It's seven eight . Take Away seven is one . | |
| 03:57 | We have 1/14 as our answer . So that's how | |
| 04:01 | you do this . They're fairly simple , right ? | |
| 04:03 | And they're much like doing edition ones . Just make | |
| 04:05 | sure when you do it , you're starting at that | |
| 04:07 | top left and going this way . Okay . Not | |
| 04:09 | not the other way because otherwise you'll get the opposite | |
| 04:12 | , you'll get the wrong answer . Okay . Kind | |
| 04:13 | a lot of difference that Six take away two is | |
| 04:17 | not the same as to take away six . They're | |
| 04:19 | going to give you different answers . Um Just one | |
| 04:21 | thing if you get mixed numbers when you're doing these | |
| 04:23 | uh have other videos that deal with these , but | |
| 04:25 | let's just go through this anyway , just for the | |
| 04:27 | heck of it . Um So say you were asking | |
| 04:29 | something like uh two and a quarter take away uh | |
| 04:35 | one and 1/3 . The first thing you have to | |
| 04:39 | do is actually change these into an improper fraction . | |
| 04:42 | Okay , I have other videos that deal with this | |
| 04:44 | , and essentially what we end up doing when we | |
| 04:45 | do this is we go two times for is eight | |
| 04:50 | plus one , is nine , And we put this | |
| 04:53 | over four . Okay , the reason for this , | |
| 04:55 | I'll just give you a really , really quick explanation | |
| 04:57 | on that . It was too Drew draw two and | |
| 04:59 | a quarter . Okay , it would look like this | |
| 05:03 | . Okay , there's my uh cut three things up | |
| 05:06 | in the quarters . Okay , There's 123 Did it | |
| 05:10 | did it did it did it . There they are | |
| 05:11 | , they're my two and a quarter . We have | |
| 05:14 | two times 4 plus one quarters . Okay , so | |
| 05:18 | nine quarters , so using that same sort of idea | |
| 05:22 | , ah better keep the same color , We're going | |
| 05:25 | to be going one times three plus one is 4/3 | |
| 05:29 | , and now we treat it the same . We | |
| 05:31 | just use this bow tie method again . Okay , | |
| 05:33 | so four threes 12 , nine times three is 27 | |
| 05:39 | 4 times 4 , 16 . Take it away , | |
| 05:43 | 27 take away 16 is 11 over 12 . Very | |
| 05:53 | good . Do you want one more of those ? | |
| 05:54 | Why not ? I Okay , so see here you | |
| 05:58 | go with this one . Okay , I'm not gonna | |
| 05:59 | get much harder this , are they ? So what | |
| 06:01 | about we do um Okay , three and 1 3rd | |
| 06:07 | . Takeaway one and 1 quarter . I was going | |
| 06:11 | to do a quarter . I think we just end | |
| 06:13 | up with 12 . So , let's do a different | |
| 06:14 | one . Let's do 1.5 . All right , so | |
| 06:17 | , let's do this , change it first into improper | |
| 06:20 | fractions three , threes and nine plus . That is | |
| 06:23 | 10/3 take away . two , And then we're going | |
| 06:31 | to go 234 , 6 . Uh two times 10 | |
| 06:37 | is 20 and three threes and nine . We're going | |
| 06:41 | to take these away . Okay , 20 take away | |
| 06:43 | nine is 11/6 . Okay ? We can take this | |
| 06:46 | a step further because 11 divided by six is one | |
| 06:49 | with five left day . We put that five over | |
| 06:52 | this number here . The six . All right , | |
| 06:54 | I'll tell you what I'm gonna do . One last | |
| 06:55 | one . I'm gonna make it there and I'm gonna | |
| 06:57 | race . You will see how good you are already | |
| 06:59 | . I'm gonna win . Okay ? And no , | |
| 07:01 | I don't know the question beforehand . So , let's | |
| 07:03 | do 5.5 and we'll take away three and one third | |
| 07:10 | ready set go . Let's go . Okay ? So | |
| 07:12 | this is 11 over to take away 10/3 . And | |
| 07:16 | we then worked this out . We're going to get | |
| 07:18 | the bottom number 6 33 . Take Away 20 is | |
| 07:23 | 13/6 , which is going to equal to and 1/6 | |
| 07:27 | and you go to win . Hopefully got the answer | |
| 07:30 | right ? When I did that , I'd better double | |
| 07:32 | check that when I do things quickly occasionally . Get | |
| 07:34 | them incorrect . So we did get 11 over to | |
| 07:38 | we've got 10/3 6 33 . Take away 20 correct | |
| 07:44 | , correct , correct . Look , I reckon I | |
| 07:46 | won that one . How'd you go ? I'm gonna | |
| 07:48 | hear comments saying you beat me . I reckon you're | |
| 07:50 | making it up anyway . See you next time . | |
| 07:53 | Bye . |
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Fractions subtraction trick - the fast way! is a free educational video by tecmath.
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