Mental math trick to work out fractions of an amount! - By tecmath
Transcript
| 00:00 | good day and welcome to take Math Channel , we're | |
| 00:02 | going to be having a look at in this video | |
| 00:03 | is going to be looking at how to work out | |
| 00:05 | fractions of an amount and how to do this mentally | |
| 00:08 | . This is a great video for trying to work | |
| 00:10 | out things in your head , but not only that | |
| 00:11 | , I think it's a really good video of your | |
| 00:13 | first starting these out and you just want to understand | |
| 00:16 | about what's going on when you are working at fractions | |
| 00:18 | amount rather than just getting some algorithm throwing out what | |
| 00:21 | is actually going on . So with this , um | |
| 00:26 | I'll just want you to an example , so an | |
| 00:28 | example , this is so we had three quarters of | |
| 00:33 | 20 . Okay , yeah , first off , let's | |
| 00:38 | have a look at these . Three quarters what three | |
| 00:39 | quarters actually mean ? So three quarters With 3/4 . | |
| 00:42 | If we imagine 3/4 of 20 . First off , | |
| 00:46 | what this means is we're getting 20 and we can't | |
| 00:48 | get up four times . Okay , we're dividing it | |
| 00:50 | into four , equal parts of 20 , divided by | |
| 00:53 | four . Is this bottom number ? Here is a | |
| 00:57 | dividing number ? Okay . And then we want to | |
| 01:00 | know what three quarters . Okay . This is saying | |
| 01:03 | that we worked out what one quarter is when we | |
| 01:05 | divided up by four . Okay . So we get | |
| 01:08 | we're gonna get five , but then we want to | |
| 01:09 | know what three lots of these quarters are , So | |
| 01:11 | three groups of them . This is a times in | |
| 01:15 | question , so you can think about this being the | |
| 01:18 | bottom number , being a dividing number , the top | |
| 01:20 | number being a timely number , you'll be just fine | |
| 01:23 | with . Okay , It's a really important thing to | |
| 01:25 | understand what fraction . Okay . Yeah . So with | |
| 01:29 | this 20 here we're gonna divide by four and then | |
| 01:31 | times by three or alternatively can times by three and | |
| 01:35 | then divide by four and different questions . Uh It's | |
| 01:39 | sometimes easier to do it one way or the other | |
| 01:41 | and you'll see this as you get along with a | |
| 01:43 | bit of practice with these . So 20 divided by | |
| 01:46 | four is five times three is and that's how you | |
| 01:51 | do these guys . Mental . Okay . All right | |
| 01:56 | . What about go through another one and you give | |
| 01:58 | this a go when we do this ? Hopefully you | |
| 02:00 | get this idea . Um What about we do three | |
| 02:04 | ft of Let's do it of 40 . Okay , | |
| 02:11 | equals so but I'm number divide top number times . | |
| 02:15 | Okay , because it's literally what we're gonna do with | |
| 02:18 | it , isn't it ? Um So what do we | |
| 02:20 | do we go ? 40 divided by five is eight | |
| 02:23 | times 383 24 . Okay , instant answer . Pretty | |
| 02:28 | cool though . So I better write that in 24 | |
| 02:31 | . How do you go with that ? Good . | |
| 02:34 | All right . What about we do one more of | |
| 02:37 | these and it will be on to some harder examples | |
| 02:39 | . Yeah . So what about uh give this one | |
| 02:42 | to go ? So see if you can get it | |
| 02:44 | before I go through my long winded explanation . What | |
| 02:47 | about we do ? Um No 5/6 or oh 42 | |
| 02:58 | . Okay . You're going to see these are all | |
| 03:00 | fairly simple at the moment because six goes really nicely | |
| 03:03 | into 42 . It goes in seven times and then | |
| 03:06 | seven fives are 35 . Okay so I'll give him | |
| 03:10 | some nice easy examples here . Okay so 42 divided | |
| 03:15 | by six or seven times five is 35 575 35 | |
| 03:20 | . And you're gonna see I've given some nice examples | |
| 03:22 | where the bottom number goes into this number really nicely | |
| 03:26 | . But now I'm gonna shy away from some of | |
| 03:28 | the steer away from this a little bit and I'm | |
| 03:30 | gonna start giving some nastier examples . Okay so what | |
| 03:34 | about we do this ? What about we work out | |
| 03:36 | now ? 3/4 and what is that ? Uh What | |
| 03:41 | about we do this out of a low number to | |
| 03:44 | start off with something like important . Okay 3/4 of | |
| 03:50 | 14 . So what's the answer to this is gonna | |
| 03:53 | be ? So we're still doing that same thing . | |
| 03:55 | We're dividing in times but this time we might actually | |
| 03:58 | actually flip it around , we're gonna do the times | |
| 04:00 | first , the dividing it afterward . So three times | |
| 04:03 | 14 . three times 14 . The answer to that | |
| 04:07 | is 42 . Okay . 42 divided by four is | |
| 04:13 | 10 and 2/4 or you know says it's 10.5 . | |
| 04:18 | Let me go through the actual answer of how I | |
| 04:20 | got this . Okay so let's have a look . | |
| 04:24 | So Quite literally we're going 14 . Well that's a | |
| 04:29 | bit big . What about we do this one ? | |
| 04:32 | You're smaller pen 14 and when times is by three | |
| 04:37 | We get 42 And then what we're doing is 42 | |
| 04:42 | divided by full and we get this answer oh 10 | |
| 04:51 | . But to over four and you might then also | |
| 04:54 | say well this actually equals 10 and Uh huh . | |
| 04:58 | Okay , because two goes into this one once until | |
| 05:01 | this one , so there's our answer . Okay , | |
| 05:04 | I'll use that just circle answer . All right , | |
| 05:08 | so it's the same sort of algorithm again and again | |
| 05:11 | , not just get a little bit trickier , that's | |
| 05:13 | all . But the idea is exactly the same . | |
| 05:16 | Okay , when you're first learning this sort of stuff | |
| 05:19 | , I think it's really handy . Especially we're gonna | |
| 05:20 | take it into a test . Remember some easy examples | |
| 05:22 | in your head that you can work with because what | |
| 05:24 | works for the simple . We'll also work with the | |
| 05:27 | hard quite often . Okay , so what about we | |
| 05:30 | do one more of these and see how you go | |
| 05:32 | . Um What about we do ? Um 3/5 of | |
| 05:41 | the I do . Okay , So once again you | |
| 05:47 | might do the times in parts first . The dividing | |
| 05:50 | part 2nd . Okay . So what we get is | |
| 05:53 | as follows . Alright . 13 13 , 18 Times | |
| 05:59 | three . OK . The answer to that is 24 | |
| 06:02 | . So we have 54 54 divided by five . | |
| 06:08 | His 10 fade for left over that four . We're | |
| 06:12 | going to put over this for fits . Okay . | |
| 06:17 | Did you get that answer ? Hopefully you did . | |
| 06:20 | Okay , so just again , just to show the | |
| 06:22 | working out this is 18 times three . This is | |
| 06:25 | 18 times three which gave us the answer of All | |
| 06:32 | right , that's in a different color here . 54 | |
| 06:36 | 50 for then divided by five . And then we | |
| 06:42 | got an answer of 10 and four ft . Okay | |
| 06:47 | . So how did you go with that ? Good | |
| 06:48 | . Yeah , hopefully did . Um , All right | |
| 06:51 | . So , anyway , that's how you do those | |
| 06:53 | any questions comments ? Uh , Good . Bad . | |
| 06:56 | I don't know . Let me know . Uh , | |
| 06:59 | Anyway , thanks for watching . We'll see you next | |
| 07:02 | time . Okay . |
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