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

Percentages - fast math lesson - By tecmath

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00:00	good day and welcome to Tech Math channel . What
00:02	are we having a look at in this video is
00:04	a way of working out percentages . Okay . This
00:07	is from a fraction or something like this . Okay
00:10	. Because percentages are just a measure of a number
00:12	out of 100 . Okay , so we're going to
00:14	look at how to do this now . First off
00:17	, I think it's really , really important that we
00:18	actually get this definition of a percentage down pat now
00:22	because I think this helps a fair bit . Now
00:24	. If you understand what percent means , you'll do
00:25	pretty good . Percent has two parts to it has
00:29	this party of the per and then we have sent
00:32	per means out of , Okay , just something out
00:36	of something else . And this sent here . Well
00:38	sent means 100 . Okay , there's 100 cents in
00:42	the dollar or there's 100 years in a century .
00:45	Most of you guys well know what ascent is and
00:47	there's 100 cents on the dollar . So it's a
00:48	really , really easy thing to remember . The percentage
00:51	symbol looks like this . Okay . It almost looks
00:54	like 100 which has been reorganized . If you can
00:57	imagine there's been a one and with two zeros here
00:58	. Okay . Maybe I'm taking a little bit too
01:00	far . Okay , so I'm going to work .
01:02	We're gonna be working . How do our work percentages
01:05	out ? So let's say for example , we want
01:08	to work out what is 15 out of 16 ?
01:13	We want to work what this is as a percentage
01:15	out . Yeah . The easiest way of doing this
01:19	is this means first off , this means 15 divided
01:22	by 60 . I think some people get thrown by
01:25	this line here . What we do is we get
01:27	this number here and we're times it by 100 over
01:32	one . Okay , This is how we change it
01:35	into a percentage now . What do we do then
01:38	? Well , we just treat these like any other
01:40	thing where we're multiplying fractions when we multiply fractions ,
01:43	we're going in top number of times the top number
01:45	and then bottom number times a bottom number to get
01:48	our answer . Okay , So 15 times 100 is
01:54	1000 500 . And this is going to be divided
01:58	by 60 Times 1 , 60 times one is 60
02:04	. Now , what we can do is we can
02:05	cancel out numbers okay , like Zeros are going to
02:11	cancel each other out . Okay , because 10 is
02:13	going to go into both of these . So we
02:14	end up with a number of 150 divided by 60
02:18	, divided by six is 25 . Okay , so
02:25	25% for 15 Over 60 is 25% . Now if
02:29	we use just before we go on and we actually
02:32	use that idea of counseling at numbers , we can
02:34	look at a number here that goes into a Into
02:36	both of these . So 15 actually goes into both
02:39	of these . Yeah , 15 goes into this one
02:41	once and it goes into this one four times .
02:44	So we would end up with a number a quarter
02:46	and a quarter is the same as 25% . If
02:49	you can imagine quarter of a dollar , it's 25
02:52	cents . Yeah , it's a nice way of thinking
02:54	. What you also might realize is this quarter here
02:57	four times 25 actually gives us 100 . This is
02:59	a bit of a common theme with this number over
03:03	up here is one . Okay , so this is
03:06	the way you work out percentages . How about another
03:09	example ? What about we um have a look at
03:15	, I'm just gonna be using some easy examples today
03:17	. So we talked about , we have a look
03:18	at the number I said before . What about we
03:20	have a look at ? 35/70 . So what do
03:25	we do with this ? You might be able to
03:27	look at straight away and go , well the number
03:29	five and then the number seven goes into both these
03:31	in fact 35 goes into both numbers goes into here
03:34	once and this one twice . This is actually the
03:35	same as a half . But let's treated we're just
03:40	trying to work out percentages here three times that .
03:42	By 100 over one , what does this equal ?
03:45	This equals 35 times 100 Is 3500 , divided by
03:54	70 times 70 times one is 70 . And we
03:58	can cancel the zeros out . So 00 And the
04:01	number seven goes into both of these . It goes
04:04	into actually , well that will tell us what our
04:06	answer is , won't it ? seven goes into 350
04:11	50 times . Okay . Our answer is 50 And
04:15	again to say what I said before 35 goes into
04:19	this once , 35 goes into 70 twice . So
04:22	And a fraction up there is the same as a
04:24	half , so half is the same as 50% .
04:27	Yeah . You want . Again Also notice that two
04:30	by 50 is 100 half of a dollar is 50
04:33	cents . Okay . Uh there's a really , really
04:37	great relationship between these . Okay , so it's a
04:39	really great thing for math to understand . I think
04:41	it's one of these recurrent sort of themes in maths
04:44	. Um So let's have a look at a couple
04:46	more examples . What about we have a look at
04:50	this example , a bit of a harder one this
04:52	time . Nothing too taxing . We're going to do
04:54	16 divided by 20 And so to turn this into
04:59	a percentage , What are we going to do ?
05:01	We're going to times it . 100 over one .
05:05	Okay , so 16 times 100 Is 1600 . We're
05:14	dividing this by 20 times one , which is 20
05:19	. Okay , We can cancel the zeros out and
05:21	start off with And then we have 160 divided by
05:25	two . Now , 160 divided by two equals 80
05:29	. So your answer is 80 percent . Now .
05:33	Just to do what I've been doing before . Number
05:36	that goes into both of these , or four goes
05:39	into both . It goes into this four times and
05:41	this 15 times . So actual we can't then and
05:44	nothing else goes in there . So fraction that this
05:48	is is 4/5 . Okay , we can't actually do
05:51	this any further . Okay , so but 4/5 of
05:54	a dollar is 80 cents . If you can imagine
05:56	1/5 divided by five is 20 cents and then times
06:00	it by four is 80 . So this is a
06:02	correct answer . Okay , So this is 80% .
06:07	Let's just go one last example . Hopefully you're going
06:14	really , really good with this and you're getting a
06:16	degree of understanding with this . What about we do
06:20	9/20 . Hopefully when you do your percentages test ,
06:25	you'll get better than nine and 20 will be really
06:27	, really good at . And you'll actually get 20
06:30	out of 20 and you get 100% because 100% is
06:32	everything . But let's have a look at . Nine
06:34	out of 20 . Sorry for daddy percentage should have
06:37	comment there . So we're gonna times this by 100
06:41	over one to turn it into a percentage . And
06:44	then what do we do ? You remember ? But
06:47	nine times 100 is 900 one times 20 is 20
06:55	. What can we do next ? We can cancel
06:57	out the zeros . Yeah , We're gonna end up
06:59	with this 90 divided by two now 90 divided by
07:03	two . If you get 90 and you cut it
07:05	in half , You're going to end up with 45
07:09	percent . Okay , this one is finally enough .
07:13	We actually can't take down anymore . There's no common
07:15	number that goes into nine and 20 except for one
07:17	and that won't actually really change our our fraction here
07:20	but our answer is 45% . Okay , which makes
07:24	sense because nine is a little less than half of
07:28	20 . Okay , so we should expect and half
07:32	is 50% . So we should expect an answer a
07:34	little bit less than 50% . So this is a
07:36	good answer now anyway . Hopefully you're really , really
07:39	good with these . I'll put some links up for
07:41	other percentage things I've got . It's really worth checking
07:44	out , especially if you're starting out with these .
07:46	But I hope that helped a fair bit . Okay
07:49	, so you next time .

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