Percentage Trick - Solve precentages mentally - percentages made easy with the cool math trick - By tecmath
Transcript
00:0-1 | Hello , Welcome to the Tech mouth channel . What | |
00:01 | we're gonna be having a look at in this video | |
00:03 | is we're going to be having a look at a | |
00:04 | way of working out percentages in your head . Uh | |
00:07 | , it's going to start out in this video , | |
00:09 | we're just gonna be looking at fairly simple percentages , | |
00:11 | say ones that have fives and tens and 15% of | |
00:14 | a number or 25% of a number or 50% or | |
00:18 | 75 , Okay . Um , just ones that are | |
00:22 | fairly simple and then we're gonna work , uh , | |
00:25 | in a later video , get onto the more complex | |
00:27 | versions . But this is a really , really great | |
00:29 | little introduction for it . So , first off , | |
00:32 | it's good to be able to understand what percentage means | |
00:34 | . Our percentage , The percentage is literally , if | |
00:39 | you see a percent Has two parts of the word | |
00:42 | here . By the way . This per means out | |
00:44 | of sent means 100 . A percentage number is just | |
00:48 | a number out of 100 . Um , so , | |
00:51 | well , without much further ado we'll see how you | |
00:54 | can go on this particular thing here . Okay , | |
00:57 | So first off , how do you go about that | |
01:00 | ? How fast could you work out ? Say 15 | |
01:03 | of I . D . Hopefully you've already got the | |
01:08 | answer . Hopefully you've got the answer of 12 . | |
01:12 | Yeah . Uh I'll tell you how I worked this | |
01:15 | out really quickly now , this works on the idea | |
01:18 | of just a couple of things and I'm gonna jot | |
01:21 | these down there . first off , I'm going to | |
01:24 | introduce the idea of 100% of a number , 50% | |
01:30 | of a number , 10% of a number And 5% | |
01:35 | of a number . Yeah , We're going to be | |
01:39 | using this a lot in this video today . 100% | |
01:41 | of a number Is the actual number itself . So | |
01:44 | an example , 100% of 80 would be 80 . | |
01:48 | Okay , 100% of 70 is 70 . of 720 | |
01:52 | is 720 . 50% of a number is half of | |
01:57 | the number is half of 100 . Okay , because | |
02:00 | these percent numbers , these are out of 100 . | |
02:03 | Okay , there's 100 and 100 sorts of full amount | |
02:05 | . This is 50 out of 100 . It's half | |
02:08 | the number . So half of 80 , 50% of | |
02:12 | 80 is 40 , of 12 is 6 , 50% | |
02:16 | of 32 is 16th . Half the number . Now | |
02:21 | we can work out 10% of a number which is | |
02:24 | 10 parts out of 100 . Really , really easy | |
02:26 | because it's the same as dividing by 10 . Um | |
02:29 | Yeah , for example , I've got three numbers sitting | |
02:34 | here , so I'm going to use these as my | |
02:35 | example . If I want to work at 10% of | |
02:37 | 15 , it's a matter of just moving the decimal | |
02:40 | place , the decimal places usually here and I'd move | |
02:42 | it back left so it become here . So the | |
02:45 | 10% of 15 would be 1.5 , 10% of 80 | |
02:50 | the decimal places here and we'd move it back one | |
02:52 | to the left , 10% of 88 , of 12 | |
02:57 | . We move it back and it becomes one point | |
02:59 | to hopefully get that idea . Okay so 10% we | |
03:03 | just divide the stomach by 10 . It's a 10% | |
03:06 | of i . d . The site , 5% of | |
03:10 | a number Is just half of 10% . So 5% | |
03:14 | here . Well before . Okay . Yeah we're just | |
03:19 | going to use this idea in this video today . | |
03:21 | So remember those these are what you need to know | |
03:24 | for working at these numbers . Okay so 15% is | |
03:27 | made up of two things . It's made up of | |
03:29 | a 10% portion And a 5% portion . Right ? | |
03:34 | You will be able to start doing these in your | |
03:36 | head by the way and I encourage you as we | |
03:39 | go along to try and work them out in your | |
03:41 | head . You might try to work them out of | |
03:42 | your head , try to work them out on a | |
03:43 | piece of paper and then see if you can get | |
03:45 | the same answer as I do . So 10% of | |
03:49 | I . D . Is I'D . 5% of that | |
03:52 | is half of this . So it's four . And | |
03:55 | then what we do is we just add these together | |
03:56 | because 10 plus five is 15 we're just adding these | |
03:59 | guys together . Eight plus four . It's 12 . | |
04:04 | We can't go through another example . Okay what about | |
04:09 | we go through um Okay just a nice one for | |
04:14 | the minute . What about we do this 1 , | |
04:16 | 60 of 42 . Yeah . What ? You might | |
04:25 | notice ? I'd pause it and try to get her | |
04:27 | to go . You might try to work out what | |
04:29 | it's made up mainly of now . The easiest way | |
04:31 | of getting there is a 50% number . If you | |
04:35 | remember that's half and I 10% number . Okay . | |
04:42 | And then you're going to add these together . So | |
04:44 | 50% is half which is 21 , If you're moving | |
04:48 | this decimal place you'll get really good doing this is | |
04:50 | 4.2 and you're adding these together . Okay ? You're | |
04:55 | gonna see outline the units up there , you'll do | |
04:57 | this in your head . So 21 and 4.2 is | |
05:00 | 25 two . All right , I'll go another one | |
05:07 | here . This is a bit of a harder one | |
05:11 | . I'm going to use the idea of 100% number | |
05:13 | here . I'll give you a bit of a heads | |
05:14 | up on this one . Oh no , work out | |
05:17 | 95% . So you might be taking something away Of | |
05:22 | 720 . Okay , so give it a go . | |
05:30 | Okay , so the idea is we're going to have | |
05:32 | 100% . Usually you wouldn't need to really think about | |
05:35 | like this is just this number here , which is | |
05:36 | 720 and we're going to take away 5% . So | |
05:44 | We have 720 . A 10% would be Moving here | |
05:48 | . The decimal place , it becomes 72.5 . That | |
05:51 | would be 36 . We're not adding this on by | |
05:54 | the way because it's 95 . This is 100 take | |
05:56 | away five . So we're actually going to take this | |
05:58 | away . So 7 20 take away 36 . Hopefully | |
06:03 | get really , really fast . These is 680 for | |
06:07 | I do have other videos where we look at how | |
06:09 | to rapidly subtract things and rapidly multiply things . Okay | |
06:14 | , so how'd you go with these ? Okay . | |
06:18 | I reckon I'm gonna put a couple more up just | |
06:20 | to give you a bit of practice . I'll tell | |
06:21 | you what I'll do , I'll put three up right | |
06:23 | now . And then what you could do is you | |
06:25 | could pause the video , try to work through and | |
06:27 | try to work through them mentally . Try to work | |
06:30 | through them on a piece of paper and then We'll | |
06:34 | go through the answers . Okay ? So check it | |
06:36 | out . We started working that mentally check your answers | |
06:38 | on a piece of paper and then we'll go through | |
06:40 | them . So what about the first one ? Will | |
06:42 | be 55 Of 360 . The next one is going | |
06:49 | to be a bit of an easy one . of | |
06:54 | 860 give you a little hit with this 25% . | |
06:58 | You can also think it was a quarter um might | |
07:01 | be a bit of a hint . I'm going to | |
07:02 | work it out both ways and we're gonna do 85% | |
07:07 | of UB 620 . All right , pause the video | |
07:13 | . Give them a guy . All right . Hopefully | |
07:17 | you pause the video . Hopefully where you've given them | |
07:19 | a go and hopefully you got some pretty good answers | |
07:21 | there . So 55% is made up of as you | |
07:25 | realize A 50% , which is half Okay , 190 | |
07:31 | plus 10% of half of that . But you might | |
07:35 | also realize that 50% you can actually just move this | |
07:38 | decimal place and get I don't Okay . Because 50% | |
07:44 | and 5% is that's just 1/10 of that . Okay | |
07:47 | , So get this answer of 198 Without 25% of | |
07:53 | 860 Yeah , you should easily work this one out | |
07:57 | . I've known a few people will straight away , | |
07:59 | they're gonna look at that and say 25% is the | |
08:01 | same as dividing by four because 25% a quarter of | |
08:05 | a number . So you might just divide this number | |
08:07 | by four and if you did that , you would | |
08:09 | get the answer . Eight divided by four is 26 | |
08:13 | divided by four is one . Then you carry the | |
08:15 | two across and you get 215 . All right . | |
08:18 | But I'm going to also work it out using this | |
08:21 | particular method . Okay , because this is all just | |
08:23 | a bit of practice as well . So 25% , | |
08:26 | you might realize it's made up of 210% and a | |
08:28 | 5% . So it's going to be 86 86.5 of | |
08:33 | 86 , which is 43 . So it would add | |
08:36 | all these together , 86 plus 86 is going to | |
08:40 | be 172 . 172 Plus than that . 43 is | |
08:48 | 215 the case . All right . That in 86 | |
08:51 | plus 86 , which is 173 . 172 , sorry | |
08:56 | , plus 43 , which gives us his answer here | |
09:01 | . Okay , so 2 15's our answer Now . | |
09:03 | What about 85% of 620 . I think the easiest | |
09:09 | way to do this one is looking at a 100% | |
09:13 | number And then getting rid of a 10 and also | |
09:18 | a 5% . This does I must say I'm not | |
09:21 | going to wear . It does occasionally get a bit | |
09:23 | tricky . And you had some of these numbers are | |
09:24 | going to be trickier than others . Okay . So | |
09:27 | we're going to start with 620 and we're going to | |
09:31 | take away 10% , which is going to be 62 | |
09:34 | . So all right . This working it out that | |
09:36 | we're thinking as we go 620 take away 62 and | |
09:41 | we're gonna take away half of this , which is | |
09:43 | 31 All up . You might think 62 and 31 | |
09:47 | is 93 . So 620 takeaway 93 Is 527 . | |
09:55 | Now , these will require a bit of practice and | |
09:57 | I'll be the first to admit for some numbers they're | |
09:59 | going to be harder than others . Okay . Some | |
10:02 | of these numbers are definitely much harder than others . | |
10:04 | Obviously , it's a lot easier to work out 15% | |
10:07 | of a number than it is to work out 85% | |
10:10 | of the number . Just based on this , this | |
10:12 | idea . Okay . Uh , anyway , do practices | |
10:15 | , you will get better at it and this is | |
10:16 | what it's all about . Trying to get better at | |
10:18 | working things mentally . The next video , what I'm | |
10:21 | going to link to right now is we're gonna start | |
10:23 | looking at say we're working out Not just with the | |
10:26 | fives and tens and that sort of deal . We're | |
10:28 | going to start looking at things like 22% or 53% | |
10:33 | or 87% . So where we get away from these | |
10:36 | divisible numbers by five anyway , thanks for watching . | |
10:39 | See you next time . |
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