Percent of a unknown number - percentage math lesson - Free Educational videos for Students in K-12

Percent of a unknown number - percentage math lesson - By tecmath

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00:0-1	Good day . Welcome to Tech Math channel . We're
00:01	going to be having a look at in this video
00:03	. We're going to be having a look at how
00:04	to solve percentage problems . Ones of the type like
00:07	this . I say you ask the question 30% of
00:12	what number is equal to 60 ? Nice , easy
00:17	one to start off with and how you would go
00:19	about solving this . So there's a couple of different
00:22	ways that I would actually solve this question . There's
00:25	a couple of different ways I would think of solving
00:26	this question . I might use one or I might
00:29	use the other depends upon how you see this .
00:31	But I think the most stock standard way of doing
00:34	this is as follows . First off , it's really
00:36	, really important to change This . To understand 30%
00:41	means 30 Out of 100 whatever in Matthew c of
00:49	It means times , so 30 divided by 100 times
00:53	this unknown number Is equal to 60 . So all
00:57	I've done is I've rewritten it out as this type
01:00	of maths question . Okay , we can go a
01:02	step further and we can go 30 divided by a
01:04	100 is equal to .3 . So we have the
01:08	percentage the fraction and the decimal . Okay ? And
01:13	I'm just going to ride it out the same way
01:15	as the .3 times this unknown number is equal to
01:19	60 . So if we have this we can now
01:22	solve this question . We want to get this by
01:24	itself . So we have to get rid of this
01:27	.3 here at the moment , this .3 is times
01:29	in by this number . So we have to divide
01:31	both sides by .3 . Okay ? So if we
01:34	do this we're gonna end up with this unknown number
01:36	and we're gonna get 60 and we're gonna divide it
01:38	by 0.3 . Okay . And if we do this
01:43	, Give it a go 60 , divided by .3
01:47	. The answer you're going to get Is going to
01:50	be 200 . Okay , so We go back to
01:55	our original , think 30% of what number is equal
01:58	to 60 , of 200 is equal to 60 .
02:03	So you see how that works first , Change it
02:04	into the fraction , change it into the decimal .
02:07	So you might even be able to skip this step
02:09	fairly quickly and change it straight into the decimal Times
02:13	. This unknown number is equal to 60 and then
02:16	you just have to get rid of this by dividing
02:18	it on both sides , gets rid of it here
02:20	divided here . And that works for the more complicated
02:23	, it works for the less complicated . It works
02:26	Okay . Another way , if you don't like that
02:28	method , you might look at it and go ,
02:29	well another way to think about this is as follows
02:33	, Okay , um personally I like that method there
02:37	, but this occasionally I find people prefer this type
02:39	of method here and that's this sort of one here
02:42	. What you might look at is you might look
02:43	at it and go 30% of what number equal 60
02:45	. So you might go , well , okay percentages
02:47	out of 100 . So what if I was to
02:50	say 1%, , What's 1% of what number Is equal
02:57	to 60 K . C If 30% what's this is
03:02	30 times bigger than one ? So this number here
03:05	has to be 30 times bigger than this number here
03:07	. What number is 30 times bigger than 60 or
03:10	60 divided by 30 is to so 1% of this
03:13	unknown number is two , But we're actually after 100%
03:18	of the number , so 100 times this number .
03:22	So I'm gonna do times you buy 100 now ,
03:24	You know , one time 200 because we're after that's
03:26	or after 100% of this number Is therefore going to
03:29	be equal to 100 times this number here . So
03:32	200 . So that's another way that you can answer
03:36	this question . It's a lot easier . I guess
03:38	if you have nice and easy numbers like 30 and
03:40	60 and that to fly around with , it gets
03:42	a little bit more tricky when you start getting nastier
03:45	numbers . But I think both methods are pretty good
03:49	. So I'm going to just chuck up another example
03:52	and it's a good one to work with . I
03:54	think I'm actually gonna probably choose the first method to
03:57	solve it . So say another nice easy question you've
04:00	got and see how you go with it is say
04:02	35% . Uh What number is equal to 90 ?
04:10	Okay , so 35% . You can change this into
04:13	35 over 100 but I'm going to skip that step
04:16	and I'm going to change it straight away into this
04:19	is the same as point 35 Times . This number
04:25	here is equal to 90 , So we divide both
04:30	sides by .35 to get our answer , so therefore
04:33	this unknown number here is the same as 90 ,
04:37	divided by 0.35 . Okay , to get rid of
04:41	it over here , we have divide both sides and
04:44	that's going to give us , Look , here's the
04:46	number I have had a little bit earlier is 257
04:51	0.1 for Okay , so if you do , if
04:54	you work that out 257.14 . And look , you
04:58	can use the same sort of method where you worked
05:00	out 1% . It's a little bit more tricky .
05:02	Okay , So that's the way that you can solve
05:05	these particular questions . And I hope that that answered
05:08	any any problems that you have with that . It
05:11	doesn't matter . It was 70% of what number equal
05:13	. 2000 , for . You could use that same
05:16	particular method . Okay ? Anyway , hopefully that was
05:21	some help . We'll see you next time . Bye
00:0-1	.

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