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

Fractions Division - fast math lesson - By tecmath

Transcript


00:01	Welcome to the Tech Math channel . What I'm gonna
00:02	be having a look at this video is going to
00:04	be looking at dividing fractions . So I'm going to
00:06	try to explain , I'm going to explain how to
00:09	do the most simple ones of these . Are we
00:11	going to work on some mixed numbers and things like
00:14	this ? And then I'll give you some examples to
00:16	work on by yourself . So how to divide fractions
00:19	? Yeah , when we're doing these , it's really
00:22	, really important to realize that dividing fractions is much
00:24	like multiplying fractions . It just involves an extra step
00:28	. Okay , so you can work out this extra
00:30	step . You have absolutely no problems doing it .
00:34	So I'll give you an example , say I wanted
00:36	to know what a quarter divided by for half these
00:45	. Okay . Yeah . How many groups of a
00:49	heart ? Really quarter ? It might seem a bit
00:51	strange to think about . Okay . And often it
00:55	is when you first start doing these , the way
00:57	that we do these is really , really simple .
00:59	And it's as follows , we basically just have to
01:03	change this part here too at times . Okay ,
01:06	we keep the quarter the same . But what we
01:09	do is we flip the denominator the new brain here
01:13	. Okay , so we flip these around and make
01:15	them change positions . We turn them on their head
01:16	, so to speak . So the two ends up
01:18	the top and the one ends up there on the
01:21	bottom . Okay . And then we multiply this out
01:24	. So one times two is to and four towards
01:30	1 is for this . We can actually , there's
01:34	another that goes into both two and four which is
01:36	two , so two goes into two once and he
01:38	goes into four twice as this is the same as
01:41	a half . Okay , so how did you go
01:45	with it ? So how many ? This might be
01:47	a way you might think about this too because in
01:49	a quarter and you want to divide it by half
01:51	. This is this is quite a difficult thing to
01:53	think about , I think when you first do in
01:55	these , but if you can imagine a quarter ,
01:58	okay , you can imagine a quarter here . All
02:01	right . And you want to see how many times
02:05	here half goes into it ? Well , it doesn't
02:09	go into it actually , only half of it managers
02:11	. Okay , we only got half this actual about
02:14	there . So this is our answer , which is
02:16	a half . Okay , you probably see if we
02:20	did it the other way and said how many quarters
02:22	in a half . In fact , let's work that
02:24	out . Maybe this this will be a good one
02:28	for you to work out if you if you didn't
02:30	quite get that . So let's do this particular one
02:32	which is have any what's a half divided by a
02:37	quarter . Okay so the way that we do this
02:43	is as follows , we start with a half ,
02:47	We're going to change this two times and this is
02:48	going to become flip these over . So this will
02:50	become four over to For over 2 , 4 over
02:57	one , apologize about that I'm making , he was
03:00	staying there , I think this is a one ,
03:02	so it goes in here , so one times four
03:04	is four and two times one is two , so
03:08	four divided by 2 , 4/2 , 4 divided by
03:11	two is two . So you might be able to
03:14	think about this , I can draw my half and
03:18	you wanted to divide this into quarters . Uh We'll
03:21	divide to see how many times quarter goes into it
03:24	. And so you'll see there's one two quarters ,
03:28	so we're seeing how many times quarter goes into it
03:30	and there's one 2/4 in there . Do you get
03:33	that ? Okay let's uh go another example . Then
03:39	I'm gonna put someone's in next numbers up and see
03:41	how you go with those . They're also pretty easy
03:43	. Okay so what about we do three quarters divided
03:47	by uh Right So we changes into 3/4 . Well
03:58	that's the same isn't it ? We changed at the
03:59	times and then we flip these guys around so too
04:03	goes up here , one goes down here And we
04:06	multiply them out . three times 2 is six four
04:09	times , 1 is four , six divided by four
04:14	equals one . And there's two left over to over
04:19	four . We can actually see there's a number that
04:22	goes into both the two of the four here .
04:24	So we get one and two goes into this once
04:27	and two goes into his four twice . So the
04:29	answer is 1.5 . Okay . Yeah . Alright How'd
04:35	you go with this ? Hopefully you're going pretty good
04:37	. I'll tell you what , I'll give you a
04:38	couple of mixed number ones to work with . Now
04:41	let's do those . What about we do So say
04:45	what is 2.5 divided by um the quarter . You
04:52	might be able to actually think . Okay . I
04:54	know the answer to that one . You might think
04:55	how many quarters are in 2.5 . Okay . Maybe
04:59	you can think about that right now . If you
05:01	can work that out anyway , I'm gonna start working
05:04	at the answer on this . So as we look
05:06	at another video is the way that we can change
05:09	this 2.5 year into . We have to change his
05:12	2.5 year . Let me start again . We have
05:15	to change is 2.5 year . This mixed number into
05:19	an improper fraction . Okay . So this will be
05:22	where it's no there's no hole number . It's just
05:24	a number over top of another number . It's called
05:26	a problem because this number at the top were bigger
05:28	than this number in the bottom will be smaller .
05:30	And the way that we do that is as follows
05:33	. It was This number times this number plus this
05:37	number . So we end up with five and we
05:39	put that over it to explain that really , really
05:41	quickly again for you guys who haven't seen my other
05:43	videos when I talk about mixed numbers to improper fractions
05:47	. If you can imagine 2.5 . Okay , there's
05:50	my 2.5 . Okay . I'll draw them as halves
05:53	here . So there's 12 that there's one there's 2.5
05:58	. You can see there's 12345 Have here . 1
06:03	, 2 , 3 , 4 , 5 . So
06:06	there's 5/2 . Okay . Now so we're not doing
06:11	that first part two times two . It's two times
06:14	two here because they have so there's 12342 to 4
06:17	plus one . Here's a stat fire bit and we're
06:20	talking about half . So this is a number that
06:22	goes on the bottom . Okay , so I'd have
06:25	two times this year . By what ? Okay ,
06:30	I'm gonna put this over , this is going to
06:31	become four over one . So let's do this 5420
06:38	and we're gonna put that Over two times 1 ,
06:41	which is to 20 divided by two is 10 .
06:45	That sort of makes sense , doesn't it ? Because
06:47	if you can imagine 2.5 , this is my 2.5
06:50	year , there would be um I'll see what colour
06:55	is it ? There's one quarter here , there's 2/4
06:58	three quarters four quarters five quarters six quarters seven quarters
07:04	eight quarters nine quarters 10/4 . Okay , so there's
07:08	10 lots of a quarter there . So how did
07:11	you go with that ? Hopefully . Pretty good .
07:14	I'll tell you what , I'll give you another one
07:15	of those if you get confused in these mixed numbers
07:18	. By the way , I have other videos which
07:20	look at these . So definitely go and have a
07:22	look on my channel for these . So what about
07:24	we do three and a quarter And I'm gonna divide
07:29	that by , I'll tell you what , I'm gonna
07:30	divide one mixed number by another mixed number . I'm
07:32	going to divide this by two and a third .
07:36	All right to it . Well , I can I
07:38	can understand if you look at that . And you
07:40	thought I have no idea what that is off the
07:42	top of my head . I'll tell you what .
07:44	I actually don't either . I'll show you how I'd
07:46	work it out . So first off I'm going to
07:48	change these into improper fractions . Okay , I'm going
07:52	to sort of do a double steps all at once
07:54	here . Um The first off we'll changes to improper
07:58	fractions . So three times four is 12 plus one
08:03	is 13 over four . And this number over here
08:09	, I'm gonna chuck the answer that's over here by
08:11	the way because and you'll see why in two times
08:13	three is six plus one is seven over three .
08:18	Okay . The reason I've chucked this over here is
08:20	because down here , which is my next part of
08:22	my working out I'm gonna time , so I'm gonna
08:23	flip this around so three over seven . So let's
08:30	have a look at this . 13 times three .
08:33	13 Times Street . The answer to that is 39
08:38	And four times 7 is 28 . Okay . 39
08:43	divided by 28 . There was one of those And
08:47	to get from 28 and 39 we have 11 more
08:50	so 11/28 . A completely horrible answer . I know
08:55	, but the correct answer . Okay , what about
08:58	to give you a couple of years to work on
08:59	by yourself ? So let's have a look . I'll
09:03	get my trusty eraser here and I'll rub this out
09:07	and I'll write up a bunch of them you can
09:09	work on . Okay ? So let's put three of
09:14	them up , 123 right down and then you can
09:19	work on them , pause it , work on them
09:20	and I'll go through the answers . So what is
09:22	half divided by a third ? What is 2 1/2
09:31	divided by a third . Let's go 3rd . The
09:36	third team and we'll go um three and 2/4 three
09:42	and two quarters same as 3.5 by the way ,
09:44	which is divided by let's make this 1 & A
09:49	Third . Okay , I'm sticking with the third .
09:51	Okay , pauses , give it a go . Okay
09:57	, so I'm going to go through the answers here
09:58	, so uh excuse me , a bit of working
10:01	out here because I'm gonna run out of room ,
10:02	so I'm gonna do a bit of working out on
10:04	the fly sort of thing . So this one third
10:07	here , first off , I'm going to change this
10:10	here to our times and if I do that when
10:15	I do that , I have to change this and
10:17	this around , so this is going to become three
10:20	and the one is going to go down here .
10:22	So one times three is three over two times one
10:27	, which is two , which is 1.5 because three
10:31	divided by two is one with one left over with
10:33	that over two . Okay , so now I'm going
10:36	to do uh this next one down here , I'm
10:39	gonna change this to at times and to do that
10:43	. I'm going to have to change this three and
10:45	put it up on top of it and the one
10:46	down the bottom three at the top and one down
10:49	the bottom . I'm also gonna have to change this
10:51	biggest number here . Okay , so I'm going to
10:53	do that as well . So two times two is
10:56	four plus one is five . Okay , The magic
11:02	of having computers and raises right makes life so much
11:05	easier , right ? five times 3 is 15 and
11:10	two times 1 is two , 15 divided by two
11:14	is 77 to 14 and there's one left over so
11:17	that becomes 1.5 . Okay , let's do this next
11:22	question . So with the magic of a raises and
11:25	that sort of deal , I'm going to do that
11:26	as well . So I'm going to change these both
11:29	. First off , I'm gonna change in proper fraction
11:32	. So three Times four is 12 plus two is
11:36	14 . Okay with that line back there and this
11:43	one here , one times three , one times three
11:48	is three plus one is four . So it's going
11:50	to become a four . They're not gonna have to
11:53	turn these guys upside down and change that to a
11:55	time . So let me do that . I'm gonna
11:57	change this to A times and I'm gonna turn these
12:01	guys upside down here . So the four is going
12:03	to go on the bottom and the three is going
12:05	to go up the top three At the top or
12:09	the bottom . Let's work on this there . 14
12:12	Times three The answer to that is 42 . Uh
12:19	, Four times four is 16 . So how many
12:22	times it's 16 go into 42 . So it goes
12:28	in twice , because Two times 16 is 32 and
12:33	there is 10 left over . It's a 10/16 .
12:36	I can take this a step further because two goes
12:38	into both of these numbers , so we're going to
12:40	get the answer of two and two guys into this
12:42	five times , and he goes into this 18 times
12:46	two and 58 So how did you go with those
12:51	? Okay . It looks like you've just been multiplying
12:52	fractions , and that's what you have been doing ,
12:54	and that's how we divide fractions . So hopefully it
12:57	did really good . Any questions ? Any comments ?
13:00	Put them up ? Okay . See you next time
00:0-1	.

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