Percentage made easy - Five percentage tricks and shortcuts - Free Educational videos for Students in K-12

Percentage made easy - Five percentage tricks and shortcuts - By tecmath

Transcript


00:0-1	get a welcome to Tech Math channel . I'm josh
00:02	. We got some math tricks for you today .
00:04	We're going to be having a look at my five
00:05	favorite percentage tricks . So sit back and enjoy .
00:08	So let's start out with this number one . A
00:10	nice easy way of estimating percentages of any number .
00:14	And this is one you can do inside your head
00:16	. So see how you go to say you wanted
00:18	to work out 30% of 60 now straight away .
00:22	You should be able to work this out . The
00:24	answer is 18 . So how did I do this
00:27	so fast ? Well , a bit of a quick
00:28	explanation . So you guys with a short attention span
00:31	, you might just want to chill or skip ahead
00:33	a minute . So here you go . 30% means
00:36	30 out of 100 . So we consider not 30%
00:39	but 10% of 60 10% of a number is 10
00:43	out of 100 which is 1/10 . So 1/10 of
00:46	60 is equal to six . All right . So
00:50	if 1/10 of 60 is equal to six , we're
00:51	looking for 30% of 60 30% of 60 is three
00:56	times as much . So six times three is equal
00:59	to 18 . Fast way of doing this . You
01:02	can literally just say three times six and you have
01:05	your answer and that's the fast way of doing this
01:08	. So , what about you try one of these
01:09	? So what about you try 20% of 130 .
01:14	So you can be able to get this straight away
01:17	. 10% of this number is just 13 . Okay
01:21	, Because 130 divided by 10 , 1 10th of
01:24	130 is 13 . So 20% . It's just gonna
01:28	be two times 13 . 2 times 13 . I
01:31	hope you got the answer of 26 . That's a
01:34	really , really crazy little trick , right ? And
01:36	sometimes it means it's a great way of estimating .
01:39	So , you know , you might have 22% of
01:41	133 and maybe you just modify a little bit just
01:46	so you get that roundabout sort of answer . Anyway
01:48	, now I'm going to get into my next math
01:49	trick involving percentage . So now for the next trick
01:53	, we're going to be looking about how to get
01:54	these percentages a little bit more precise and then we're
01:57	gonna have a look at things like percentage increase and
02:00	discount . So for trick number to say we were
02:03	trying to work out say something like 65% of 30
02:08	And how we go about doing that . Now ,
02:09	hopefully very quickly you'd be able to get this answer
02:12	of 19.5 . So how do we do this ?
02:16	It's pretty simple , right ? We know that 10%
02:19	of 30 is equal to three . 5% is equal
02:23	to half of this . So half of three is
02:25	1.5 . So , there's not much of a modification
02:28	that we need to make to do this , 60%
02:30	of 30 is six times 36 times three is equal
02:33	to 18 . And then we have this 5% here
02:36	. We're just going to add that on 18 plus
02:39	1.5 . There is equal to 19 .5 . So
02:43	, it's really , really a nice way of doing
02:45	this . What about I give one of these for
02:47	you ? So , I'm going to give you a
02:49	nice easy one . What about I give you 45%
02:53	of 20 . All right . You should be able
02:56	to get the answer pretty quick for this one The
02:58	first , but you're going to do well , you
02:59	probably just going to go , okay , four times
03:01	two , and that's going to deal with that .
03:02	40% or 24 times two is equal to eight .
03:06	And then what you're gonna do is you're gonna add
03:08	that to half of this 10% amount , So half
03:10	of two is equal to one . So then what
03:12	we have to do is one plus eight . We
03:14	get the answer of 9 45% of 20 is equal
03:18	to nine . Anyway . Trick number three , let's
03:20	get on to that . And what I'm about to
03:22	show you right now for trick number three , that's
03:24	not actually a trick . Just a bit of a
03:25	heads up , which I think is worth knowing if
03:27	you're doing percentage and you probably know this already .
03:30	Uh It is this what you can do when you're
03:32	doing percentages . You can rotate questions if that makes
03:35	them a bit easier . The same way that you
03:37	can rotate multiplication questions if that makes it easier ?
03:40	Always band like 86 is always preferred . 6/8 .
03:43	Even though it's exactly the same question To say ,
03:46	we wanted to work out 32% of 50 . Now
03:50	, what she may or may not be aware of
03:52	is that this can be rotated ? Like I just
03:54	said this is the same as 50% of 32 .
03:59	They're going to equal each other . All right ,
04:00	and equals exactly the same amount . So what is
04:03	50% of 32 ? Well , that's pretty simple because
04:06	50% . Just minutes , half . Okay , so
04:09	what's half of 32 ? The answer to this is
04:11	16 . So , if you have to look for
04:13	ways that you can turn these around and make it
04:16	easier for yourself , what about to give one to
04:18	you ? What about you do 33% of 20 now
04:24	? This might be a bit easier if you think
04:25	about this as being what is 20% of 33 ?
04:31	Okay , so 10% is going to be 3.33.3 times
04:36	to well this is equal to 6.6 and look that's
04:40	fairly self evident . You probably might be able to
04:41	work that out anyway . Just give me a bit
04:43	of a heads up on that . I think anything
04:45	you know on these that helps you out only what
04:47	we're going to get to is percentage increase and decrease
04:50	. I'm going to start off with decrease because I
04:51	think that's the most handy one . Okay percentage decrease
04:55	. Say you're shopping and there is a 30% off
04:59	sale . Okay so we're going to take off 30%
05:01	and the initial price is $70 . How are you
05:06	going to work out what this is now ? You
05:07	could go what is 30% of 70 or 70% of
05:11	30 same thing . And you can say , okay
05:13	seven threes a 21 and we're going to subtract that
05:17	from this initial amount , $70 take away $21 is
05:20	equal to $49 . A different way that we could
05:24	approach is as follows . We can think , okay
05:26	, well 100% of this number is 7100% of the
05:30	whole amount is $70 . Don't worry , you don't
05:32	have to do all this working at each time .
05:34	Just giving you a bit of a background . So
05:36	100% is $70.30 percent were taking off , so 100%
05:41	. Take away 30% is equal to 70% . So
05:45	really what we're trying to work out is we're trying
05:47	to work out what is 70% of $70 . The
05:52	way you can do this . Okay , so 7/7
05:54	are equal to 49 . So what do we do
05:57	there ? I literally went 100 take away 30 is
06:00	equal to 70 , 70% of 70 is equal to
06:05	49 . And I reckon that's a fair bit faster
06:07	affair , Rhodesia . It just makes the calculations go
06:10	a bit better . I think you get one of
06:12	these . What about you do one where you're walking
06:14	along and it's a 20% of sale and the initial
06:18	price is what about $120 ? You reckon you can
06:22	work this out ? All right . So , we're
06:24	gonna start with this percentage here . So we're going
06:26	to go 100% . Take away . 20% is equal
06:29	to 80% . So , we know what we're gonna
06:31	do is we're gonna be dealing with the eight multiplied
06:34	by This first party the 10% part . Well ,
06:38	this is eight times 12 , which is equal to
06:40	$96 . All right , nice and easy . Right
06:43	. All done . So , how do you think
06:45	we're going to do a trick for percentage increase ?
06:47	Well , it's pretty much the same idea . Okay
06:49	, So imagine that you had something like , uh
06:53	, you know , $30 and you wanted to increase
06:56	this by . Nice . Easy 10% . Now you
06:59	can work out 10% 10% . Pretty easily . You
07:02	can go three . So 30 plus three is equal
07:04	to 33 but you can treat this the same way
07:06	and you can say , okay , this is also
07:08	the same as 10% plus 100% which is equal to
07:12	110% . We would end up with three times 11
07:16	. 3 times 11 is also 33 . I personally
07:19	think I would actually rather work at the centre Gin
07:22	Adenine . just get lower numbers . It's easy to
07:25	deal with . But you know , horses for courses
07:26	, I guess on that one . What about I
07:28	give you one for this ? And you may argue
07:30	very simply that it's possibly easier to do this one
07:34	. Just doing it where you work at the percentage
07:35	and , and , and I'm willing to cop that
07:37	criticism on this one to say you had $150 enter
07:42	this . You wanted to add 30% . So what
07:46	are we going to do here ? We literally be
07:47	going , this is 15 . We know we're going
07:50	to be multiplying this by 100 plus 30 which is
07:53	going to become 13 . Okay , so 15 times
07:56	13 is equal to $195 . Once again , you
08:00	might find this a bit simpler just to say ,
08:02	okay , 30% while 10% is going to be 15
08:05	3 times 15 is 45 plus 1 51 95 .
08:09	It depends what you want to do with that .
08:10	Anyway . I think that these are the best percentage
08:13	tricks out there . What do you think ? Well
08:15	, you tell me in the comments If you like
08:16	this video , please give me a big thumbs up
08:18	and I always do love to hear from you ,
08:20	so I'll see you next time and thank you for
08:22	watching . Bye .

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