Percentage Trick - Solve precentages mentally - percentages made easy with the cool math trick - Free Educational videos for Students in K-12 | Lumos Learning

Percentage Trick - Solve precentages mentally - percentages made easy with the cool math trick - Free Educational videos for Students in k-12


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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