Percentages of a number - fast math lesson - Free Educational videos for Students in K-12

Percentages of a number - fast math lesson - By tecmath

Transcript


00:0-1	Good day and welcome to Tech Math Channel . In
00:02	this video , we're going to be having a look
00:03	at how to work out percentages of a number .
00:06	Okay ? Or , you know , for example ,
00:08	how you're working at 10% of a number or 20%
00:11	of a number . This is looking at it doing
00:13	in the standard way that you probably learned at school
00:15	also have some videos which are looking at some different
00:18	ways of doing this . I'll put the links up
00:19	for these now . Okay . But this is in
00:21	response to somebody actually asking for just a video on
00:23	the standard by working out percentages of numbers . So
00:25	here we go . Uh , first off , I
00:28	think it's really important , um , that you understand
00:31	what per cent means . Per cent literally means a
00:36	number which is out of or divided by out of
00:41	consent means 100 . Okay , so centers in cents
00:45	on a dollar , there's 100 cents on a dollar
00:47	or century . There's 100 years in a century .
00:50	Okay , so I think it's a really important .
00:52	First off you're realizing it per cent means Out of
00:56	100 or especially in maths terms , maybe the word
00:59	divided by 100 . Okay , so just keep that
01:02	in mind and we'll get back to that . Okay
01:05	, So an example of this might be a question
01:08	where you get to say something . What is Uh
01:12	what about 40 percent of 500 ? Okay . We'll
01:18	start with a nice easy once I say you are
01:20	asked to work 40% out of 500 . Now There's
01:25	a couple of ways you can work this out .
01:26	But the standard way of working this out is as
01:28	follows , the first thing you do is you get
01:30	this number here is 500 and being percent . Remember
01:36	that means divided by 100 . The first step which
01:39	I do is I divide this number by 100 .
01:43	Okay , so 500 divided by 100 . You cut
01:47	up into 100 parts . Okay ? And this equals
01:50	500 divided by 100 equals five . Now you're trying
01:55	to find out what 40% ? Like what's 40 parts
01:58	of these ? Okay , so 40 times five Equals
02:04	200 . So that to answer 200 . Okay ,
02:07	another way that you've probably been shown in the past
02:09	or possibly it works at the same sort of thing
02:12	with this is you might have been shown at this
02:13	way where you get , You divided by 100 .
02:17	Okay , that's what that looks like . They're so
02:19	40 divided by 100 . And then you were times
02:21	in this by 500 over one and you're gonna say
02:26	, hey wait so we did the opposite way we
02:28	did it where we got 500 we divided it by
02:31	100 and then times it by 40 . This leads
02:35	to the same sort of answer . Okay . Okay
02:37	. So it doesn't actually matter which one you divide
02:40	by 100 . Okay . All right . So I
02:43	don't want to lead to any confusion there . All
02:45	right . But this is the way I like to
02:46	think about . I like to think about this is
02:48	the number which is actually being cut up into 100
02:50	parts , but that's just the way I think about
02:53	it . Okay , so let's have a look at
02:55	another example here . So let's have a look at
03:00	ah say we'll get rid of that . Let's have
03:03	a look at say what about we do 10% of
03:10	90 . Okay . So remember again , we're cutting
03:15	one of these numbers up into 100 parts . Whether
03:18	or not you decide to do it to this one
03:19	or two . This one is actually irrelevant . As
03:21	long as you cut this one up you times that
03:23	by this or if you cut this one up 200
03:25	bits a few times by this , it actually doesn't
03:27	matter . Okay , but again , I like to
03:29	cut this one up I guess it doesn't matter but
03:31	it matters to me . So 90 Divided by a
03:34	100 for you guys who are good with dividing by
03:37	100 and 90 divided by 100 . This is a
03:40	nice simple calculation . All you're doing is there's 12
03:43	zeros here , you're moving the decimal place which is
03:45	here two times you're dividing . So the numbers get
03:48	smaller . one two because the decimal places here ,
03:53	so we end up with .9 and if you remember
03:57	where times in this by 10 . Okay , so
04:01	.9 times 10 Okay , again we're just times it
04:05	by 10 and then I'm going to get bigger and
04:07	the decimal place is going to move One time this
04:10	way , so our number , our answer becomes nine
04:14	. So again , how would you write this out
04:15	? The standard way ? You might write this out
04:18	like this , you might actually right this as 10
04:22	over 100 Times 90-1 . Where what you did is
04:28	you went 10 times 90 is 900 and 100 times
04:32	one is 100 . So 100 900 divided by 100
04:37	Equals nine . Okay , it's the same answer .
04:39	Okay . And I think it's really handy that you
04:41	actually sort of can do this , that you can
04:43	do with this with the numbers that you can actually
04:44	think about them as being like this . Okay .
04:47	Uh you know , this is the different ways you
04:49	can approach exactly the same question , so to speak
04:52	. Okay , what about this one ? What about
04:54	we do ? 15% of 110 . Okay , so
05:01	15% of 100 and 10 . Okay . Remember there's
05:04	two ways that I can sort of attack this ,
05:06	but I'm going to do it my way first .
05:08	But I like to cut up this , I'd like
05:10	to divide this number here by 100 . So I
05:12	like to divide it by 100 and I get the
05:14	answer moving the decimal place 12 times of 1.1 .
05:19	Okay . And then I'm times in this number By
05:23	15 , so 1.1 times 15 Now , hopefully you're
05:28	very good at these . The answer to this is
05:30	going to be one 65 Okay . And Hopefully that
05:39	should one . So it's 6 16.5 losing the plot
05:42	here . There's one decimal place here . So this
05:44	is actually gonna be 16 .5 . Okay , I
05:48	apologize for that . Okay , so it's always good
05:52	with that . Occasionally . I just want to look
05:53	at your answer I think . Is it realistic ?
05:54	You know ? Hey , wait a second , I'm
05:56	15% . It's a part of 100 and 10 .
05:58	It's not going to be bigger than that . Okay
06:00	, so yeah , good to revise your answers sometimes
06:03	. What most came close to making a big mistake
06:05	, but Okay , let's have a look at this
06:07	, how you do this , the standard way .
06:09	Okay . You might also be used to doing okay
06:12	. So what we'll do is we'll go 15 over
06:16	100 times 110 . A lot of people put this
06:22	over one and then what you do is you get
06:24	equals 15 Times 110 , which is going to be
06:28	1650 . Okay . For you doing 11 . This
06:35	is a basic 11 times table . There's a bit
06:36	of a trick for doing that . He said ,
06:37	look on my channel , you want to see that
06:39	divided by 100 and this equals again , it's moving
06:43	the decimal place 1 2 times . So 16 0.5
06:49	. Okay . What about one last one of these
06:55	? Okay . Trying to do these yourself too by
06:59	the way , I think you're probably okay . So
07:01	what about we do uh getting too excited already .
07:05	I want to cross that out . I think we
07:07	work at uh 6% of was about to put it
07:11	over 100 straight away because it's it's often I think
07:14	about it being 6 100 as well . Um What
07:17	about 6% of uh let's do 45 . Okay ,
07:23	so how are we going to work this out ?
07:25	So what we're gonna do is we're going to there's
07:29	two ways we can attack this possibly want to pause
07:31	it and give both ago . Okay . Both are
07:33	equally as valid . Um So what I do with
07:35	this is again , I would get this number and
07:38	I would divide it by 100 and I'm going to
07:39	end up with the answer , moving the desks in
07:41	place 12 times of 0.45 And then what I'm gonna
07:46	do is I'm gonna times it by this number six
07:50	. So what's the answer we get with that ?
07:52	Well , you might realize that where we can double
07:54	this and get .9 and it's gonna be the same
07:56	as telling them by three . So we're going to
07:57	end up with the answer of 2.7 . Okay ,
08:01	couple you guys might , I end up getting a
08:03	calculator , I do one of my maths tricks for
08:05	doing this . Okay , so hopefully you've got the
08:07	answer of 2.7 so hey , young with those ,
08:11	I'll just do that again the standard way um and
08:14	hopefully get the same answer just to double check .
08:16	So um let's have a look at this . So
08:20	okay , we go six over 100 Times this by
08:25	45/1 and this is going to equal six times 45
08:30	. The answer to this is going to be 270
08:35	and divided by 100 and divided by 100 12 This
08:41	is going to be moving the decimal place 12 times
08:44	. So the answer is 2.7 and that's the way
08:48	you can deal with percentages . Now throughout this ,
08:51	I put a little link up um and this is
08:53	for looking at a way that I think it's a
08:55	, it's a better way of working these out mentally
08:58	. Okay , so hopefully what you can do is
09:01	you can go have a look at this and it
09:03	will be a bit of a help . Okay ,
09:04	So this is different ways . Looking at percentages .
09:06	I think it's a really good way of doing it
09:08	. Okay , So hopefully that helped see you next
09:11	time .

Summarizer

DESCRIPTION:

OVERVIEW:

Percentages of a number - fast math lesson is a free educational video by tecmath.

This page not only allows students and teachers view Percentages of a number - fast math lesson videos but also find engaging Sample Questions, Apps, Pins, Worksheets, Books related to the following topics.