Learn to Subtract Fractions (Adding & Subtracting Fractions) - Part 1 [11] - Free Educational videos for Students in K-12

Learn to Subtract Fractions (Adding & Subtracting Fractions) - Part 1 [11] - By Math and Science

Transcript


00:0-1	Hello . Welcome back here . We're talking about subtracting
00:03	fractions again with like denominators , this is part one
00:06	. So I told you before and I'll say it
00:08	again in order to add or subtract any fractions .
00:12	The denominator is the bottom numbers of the fractions have
00:15	to be the same thing . So when we added
00:17	fractions earlier we had to have the denominators the same
00:20	in order to do anything and we're doing the same
00:22	thing here . So it's very very similar to adding
00:24	fractions . We kept the denominator the same in our
00:27	answer and we just added the enumerators . The top
00:30	numbers together here , it's going to be the same
00:32	thing except we'll be keeping the denominator the same just
00:36	like before . But here will be subtracting the enumerators
00:39	. That's the difference , adding and subtracting fractions are
00:42	actually very very similar to each other . In one
00:44	case we add the numerator here , we're going to
00:46	be adding the denominators . So let's get some practice
00:49	uh here and we'll use our magnets as we go
00:52	along here to get some additional so we can understand
00:54	what's going on . Let's take a look at the
00:57	fraction 4/5 and we want to subtract from that ,
01:02	the fraction 3/5 . So the first thing we do
01:05	is we check our , the denominator is the same
01:07	. In order to add or subtract fractions . The
01:10	denominators must be the same . We'll talk a little
01:13	bit more about why in just a minute . But
01:14	for now keep the denominator the same in your answer
01:18	. The denominator has to be a five . You
01:20	do not subtract the denominators , you keep the same
01:24	denominator in your answer . Just like for adding ,
01:26	we keep it here Now in the numerator which is
01:29	the top , we have a four and a three
01:31	but we have a minus sign . So it's four
01:33	minus three . So instead of adding them we basically
01:36	subtract him . It's very very simple . Four minus
01:39	three as you know , is one . And then
01:41	of course five stays along for the ride . 1/5
01:44	. And then we ask ourselves can we simplify this
01:47	fraction by dividing the top or the bottom or the
01:50	top and the bottom of the fraction by the same
01:52	number . We really can't do anything , we can't
01:54	divide top and bottom by anything that's going to make
01:56	these numbers any smaller . So 1/5 is the final
01:59	answer . So let's talk about why this makes sense
02:02	. Right ? So here we have four out of
02:04	five pieces of a pizza . So we have a
02:06	pizza cut into let's go ahead and call it five
02:09	pieces . So 1/5 2 5th , 3 fits four
02:12	fits here is 5/5 . That's what we have a
02:15	pizza cut into five pieces . But here we have
02:18	four of those five pieces . 1234 That's what we
02:21	have here , this is how much pizza we have
02:24	. Now here we have three out of five pieces
02:27	of pizza . So let's build another pizza . There's
02:29	one , there's two , there's three , there's four
02:32	and there's five . So here's another pizza again ,
02:34	cut into five pieces . But here I only have
02:37	three of them . 123 So what we're saying is
02:41	we have four out of five pieces of a pizza
02:43	. And here we have three out of five pieces
02:45	of a pizza , but instead of adding them together
02:48	, making it larger , what we're gonna do is
02:50	subtract them . Think about it . If you have
02:52	four pieces of something and you take away three pieces
02:55	of something , then you only have one piece left
02:58	. And here we're saying we have four pieces of
03:00	pizza . The five tells us how big the slices
03:03	are basically . We have four of them here and
03:05	we have three of them here , we subtract them
03:08	. And so what we actually get when we subtract
03:10	them four minus three is one , which is the
03:12	answer 1/5 here . Because if we start with this
03:16	and we take away three of those pieces like this
03:19	, what are we left with ? Only one piece
03:21	left ? Addition would be if we add these together
03:24	, subtraction as we take this amount and we take
03:26	it away , we only have that one piece left
03:29	, so we have 1/5 there . So that's why
03:32	when we take when we check to make sure the
03:34	denominators are the same , we keep the same denominator
03:37	in our answer because I've been telling you before that
03:39	I want you to start viewing these fraction wedges as
03:42	things that you can count . You don't really want
03:45	to add or subtract wedges of different sizes , I
03:48	mean you could but they're different , they won't make
03:50	a lot of sense to add one third or subtract
03:53	one third and 1/4 because the size of the slices
03:57	there would be different here , all the slices of
03:59	the same thing . So it's a simple matter of
04:00	just subtracting them or adding them together . That's why
04:03	we keep the same denominator in the same , because
04:06	here we have four out of five pieces , we
04:07	take away three out of those five pieces . How
04:10	many do we have ? Left ? One out of
04:12	five pieces of the pizza ? Uh there . And
04:16	of course we try to simplify that and we really
04:18	can't uh simplify any further . So we're done .
04:20	Right , alright , let's go on , I'm gonna
04:23	leave this up here , we'll kind of kind of
04:26	refer back to it later . Let's take a look
04:27	at the next problem . Let's say we have 3/4
04:31	And we want to subtract from it 1 4th now
04:34	again the first problem have the problem written on its
04:37	side horizontal like this . You can also see the
04:40	problem stacked on top of each other , It's fine
04:42	. Either way . Now we check four and four
04:45	. Those are the denominator , so we keep the
04:48	same denominator , We don't subtract them , we don't
04:49	add them , we keep the same denominator , There's
04:52	a four down here . Now what do we have
04:54	on top three minus ? Because there's a minus 13
04:57	minus one that goes in the numerator instead of adding
05:00	them , we subtract them three minus one is 22
05:03	out of four pieces . Now , what this is
05:05	telling us is if we have three out of four
05:07	pieces of a pizza and we take away from that
05:10	one out of four pieces then we should have two
05:12	pieces left over three pieces minus one piece . Should
05:15	give us to pieces out of four , which tells
05:18	us the slight how big the slices are there .
05:21	But we check is this fully simplified ? No it's
05:24	not because we can divide the top and the bottom
05:27	by two because those are both even numbers . So
05:30	let's take and divide the top by one . I'm
05:33	sorry not by one , we're gonna divide the top
05:35	by two and we'll also divide the bottom By two
05:39	. We divide top and bottom by whatever we want
05:42	. Two divided by two is one and four divided
05:44	by two is 22 times two is 41 times two
05:47	is two . So we think the answer is one
05:49	half . Does this make any sense ? Let's check
05:52	it out . Let's build this here . What we're
05:54	saying is that this is 1/4 of a pizza ,
05:58	2/4 of a pizza , 3/4 of a pizza and
06:01	4/4 of a pizza . We've cut the pizza into
06:03	four equal slices , but we only have three of
06:07	those slices . So this is actually how much pizza
06:09	we have in the top fraction . The bottom fraction
06:12	is 1/4 . That is this amount of the pizza
06:15	, one out of four slices instead of adding them
06:17	together . If we add them together we would just
06:19	put it over here , would actually make a whole
06:21	pizza if we add them together , but we're not
06:23	we're taking away one slice from here . So it's
06:25	like you take away one slice . What do you
06:27	have left ? You have this ? You have 1/4
06:30	2 4th , so we have 1/4 . To force
06:34	this is what you get whenever you subtract it ,
06:37	because if you start with three out of four pieces
06:39	and you take one of these away , you have
06:41	this much left which is two out of four pieces
06:44	. But you can see right away that two out
06:46	of four pieces of anything is exactly the same as
06:48	one half . You can actually see , it represents
06:51	the same amount . So the answer is to force
06:54	That's correct . That's a perfectly fine way of saying
06:56	it . If you start with three pieces and you
06:58	take away one piece , you should only have two
07:00	pieces left . Out of out of uh out of
07:03	four pieces of the pizza slice into four slices .
07:05	But a simpler way to write it is as one
07:08	half . This represents the exact same amount of pizza
07:11	as that . All right , So I think I'll
07:14	do one or maybe two more where we use our
07:16	magnets , but more or less now I want to
07:18	take the training wheels off and just solve the problems
07:21	without using the magnets are really good to visualize but
07:24	we do have to get good at doing this without
07:26	putting magnets in place and counting anything . So what
07:29	do we have ? Next problem is going to be
07:32	uh 8/9 and we're going to subtract 1/9 we're subtracting
07:38	fractions , The denominators must be the same and they
07:40	are . So the denominator of our answer will be
07:42	a nine next eight -1 . Those are the numerator
07:48	eight and one , so we subtract them 8 -1
07:50	. And what do we get ? Eight minus one
07:51	is seven and it's out of nine pieces . So
07:54	if you start with eight out of nine pieces and
07:56	you take away one out of nine pieces then you're
07:58	only gonna have seven pieces left of course out of
08:00	979 And you cannot simplify this any further because you
08:04	can't divide top and bottom by anything to make that
08:06	simpler . So we just say that's the final answer
08:10	. Mhm . Alright , problem number four . Let's
08:13	say we have 7/10 and we're subtracting from that 4/10
08:20	. All right . What do we have the denominators
08:23	here ? 10 and 10 . They're the same denominator
08:25	, so we keep the same denominator in the answer
08:28	. Then we have a seven and a four and
08:30	of course there's subtracted . So the numerator is 7
08:32	-4 , what do we get ? 7 -4 Is
08:35	three . And so it's three out of 10 pieces
08:38	, three out of 10 pieces . So it makes
08:40	sense if you start with seven out of 10 pieces
08:42	of a pizza and you take away four slices .
08:45	You start with seven slices and you take away four
08:47	slices , you should have three slices left of course
08:50	out of 10 . And so is this fully simplified
08:53	? Can we divide top and bottom by something To
08:56	make it simpler ? And we can't because this is
08:58	an odd number and this is an even number and
09:00	we can't divide top and bottom by two or by
09:03	three or anything else . So it's just three out
09:05	of 10 . Now , this will be the last
09:07	problem where I kind of use the magnets to help
09:09	us kind of visualize , I do think it's worth
09:11	doing , but after this one , we're not going
09:13	to basically do this anymore . So there's 1 10
09:16	to 10 3/10 . 4/10 . Here's 5/10 . Here's
09:20	6/10 there is 7/10 . So this is the amount
09:24	of pizza represented by this fraction . This is 4/10
09:27	. 1/10 2 10th , 3/10 . 4/10 . What
09:32	this thing is staying here is if you start with
09:35	this much . Pizza seven out of 10 slices And
09:37	you subtract four out of 10 slices . Subtract this
09:41	much , then it would be starting with this and
09:43	taking away this amount of pizza and pulling it away
09:46	. What do you have ? Left three out of
09:48	10 slices ? If you start with this amount and
09:51	you take away the four slices , you have three
09:54	out of 10 , that's basically what that means .
09:56	Now , I am going to go ahead and just
09:57	kind of leave this up here . We'll kind of
09:59	why not just leave it there ? But we're not
10:01	going to use the maggots anymore because it's very important
10:04	for you to get good at this without , you
10:06	know , drawing pictures . I think it's good to
10:08	do . But we don't want to do it for
10:09	every problem . All right , let's go over here
10:13	and solve the next problem . Let's say we have
10:16	3/7 and we'll subtract from it 1/7 . All right
10:22	. The denominator is a seven and a seven .
10:24	So denominator is the same . We keep it in
10:27	the answer . We have a three and a one
10:29	, which means we subtract three minus one . What
10:31	do we have ? Three minus one is two out
10:34	of seven . Can we simplify this ? No ,
10:36	we can't . We can't divide top and bottom by
10:38	anything else to make this simpler . So , we
10:41	keep the answer is two out of seven pieces .
10:43	Okay , that was problem number five . Actually ,
10:47	that was the halfway mark . Let's take a look
10:50	at problem number six . Let's say we have seven
10:52	out of 12 slices of pizza , and we'll subtract
10:56	three out of 12 . Now , the denominators are
10:58	the same , so , we keep it in our
11:00	final answer . And then we subtract the top number
11:03	seven minus three . So , over here we'll have
11:05	seven minus three When you do 7 -3 , what
11:08	do you get ? You get four and of course
11:10	it's still out of 12 pieces . And then you
11:13	ask yourself , can I simplify this ? Can I
11:14	divide top and bottom ? Well actually I can divide
11:16	top and bottom by four . I could also divide
11:19	top and bottom by two . That's fine too .
11:21	But if you divide by two then you'll get some
11:23	other answer and you'll be able to divide by two
11:26	again , you'll have to do it two times that's
11:28	fine . There's nothing wrong with it . But let's
11:30	you know , let's just we can recognize we can
11:33	take 4/12 and divide the top and bottom by a
11:36	larger number . We can divide by four , both
11:40	divisible by 44 divided by four is one and 12
11:44	divided by four is three because three times four is
11:47	12 . And so the answer we get is one
11:49	third . So if you start with seven slices out
11:52	of 12 and you take away three slices , then
11:54	you're going to have four slices left . This is
11:57	the right amount of pizza , but this is just
11:59	a simpler way to write the exact same amount of
12:01	pizza . So that's the final answer . Yeah .
12:05	All right , let's take a look at problems seven
12:08	. Take a look at 5/8 and we'll take away
12:11	subtract from that 1/8 . The denominators are the same
12:15	. So because we're subtracting will keep that in our
12:17	final answer and we have five minus one . So
12:20	we have five minus one . In the numerator ,
12:23	5 -1 as you know , is four and then
12:26	we have eight . Now , can we simplify this
12:29	? Where we can divide top and bottom by four
12:32	. You could also divide by two but then you
12:34	would get something , you would have to divide by
12:36	two again . So let's do it that way ,
12:38	let's not do the same exact thing every time we
12:40	know we can divide by um we know we can
12:42	divide by four because four certainly works but let's divide
12:46	by two just to get some variety here , four
12:49	divided by two is 2 and eight divided by two
12:52	is 4 , So we get 2/4 but we see
12:55	okay we can divide by two again . So let's
12:58	go ahead and divide this by two and divide this
13:00	by two and two divided by two is one and
13:04	four divided by two is two . So you get
13:07	one half . So is this fully simplified ? Yes
13:10	, I can't make it that any simpler . And
13:12	you also should ask yourself , doesn't make sense .
13:14	The answer I got was four out of eight pieces
13:17	. If I have eight pieces and I have four
13:19	of those pieces then I have half the pizza .
13:22	That's what we have here . But that's the same
13:24	thing as what we got here . Two out of
13:25	four pieces . We simplified it again , Here's 2/4
13:28	is also a half which is also 4/8 as a
13:32	half . It all means the same amount of stuff
13:34	. It's just that the fraction looks a little bit
13:35	different . All right . We have only three problems
13:39	left . What do we have here ? Let's take
13:43	a look at five tents And we'll subtract from that
13:47	3/10 . These denominators are the same there . 10
13:52	. So we keep the denominator of the same at
13:54	10 and we have a 5 -3 in the numerator
13:57	, 5 -3 . What is 5 -3 ? That's
14:00	going to be too . And then you have 10
14:02	here now , this is the final answer . That's
14:05	great . But can you simplify it ? Yes ,
14:07	you can . They're both divisible by two . So
14:09	we'll take the 2/10 and we'll divide the top and
14:13	bottom by to divide this by two . We can
14:16	divide this by 22 divided by two is 1 ,
14:20	10 , divided by two is five . And so
14:23	the answer is 1/5 . We get 1/5 of the
14:25	answer . So if you start out with five pieces
14:28	out of 10 and you take away three pieces or
14:30	slices , then you will only have two slices left
14:33	out of a 10 slice pizza . Right ? That's
14:35	correct . But a simpler way of writing the same
14:37	amount of pizza is just to cut a new pizza
14:40	into five slices and only take one . It's the
14:42	same thing . All right , so homestretch only two
14:48	more problems and here's the next one . What about
14:51	8/12 ? And we'll subtract from that 3 , 12
14:56	. The denominators are the same , which is 12
14:59	. So we'll go ahead and keep that in our
15:01	final answer . And the numerator , we have eight
15:03	and a three and it's minus . So it's eight
15:05	minus three . In the numerator , eight going down
15:09	7658 minus three is five . And you get 5
15:12	12 . Can you simplify this ? No , we
15:14	can't . We cannot divide top and bottom by something
15:17	to make these numbers simpler uh smaller . And so
15:21	we just say 5/12 is the final answer . All
15:25	right . Now we have our very last problem .
15:28	We have eight 9th and we're subtracting from it five
15:33	nights . First thing we check our the denominators the
15:36	same . Yes they are . So we keep it
15:38	in the final answer . And then on top we
15:40	have an eight minus five . So we write that
15:43	is eight minus five , what is eight minus five
15:45	? When you subtract that , you get a three
15:47	and you get of course out of nine pieces .
15:49	So if you start with eight pieces and out of
15:52	nine and you take away five pieces of course when
15:54	the pizza sliced into nine pieces , you will have
15:56	three pieces left . But this can be simplified ,
15:58	we can divide top and bottom by three . So
16:01	let's take that 3/9 and they're both divisible by three
16:06	. So we'll divide by three , divide by three
16:08	, three divided by three is one and nine divided
16:11	by three is three . So you get the answer
16:13	of one third . So the answer we got of
16:15	three nines is correct . But to make it simpler
16:18	, this is a simpler way of writing the same
16:20	exact amount of pizza and you write that as one
16:23	third . So here we have conquered the idea of
16:25	subtracting fractions with like denominators , you can see it's
16:29	the same process as edition . Other than the fact
16:32	that when we subtract , we have to subtract the
16:35	numbers on top enumerators instead of adding them . But
16:38	the denominators have to be the same to subtract them
16:41	just like for addition and we keep the same denominator
16:43	in the answer , just like addition . And we
16:46	just subtract enumerators and simplify the answers . So I'd
16:49	like you to practice all of these yourself . Follow
16:51	me on the part two and we'll wrap up the
16:53	concept of subtracting fractions when they have like denominators .

Summarizer

DESCRIPTION:

OVERVIEW:

Learn to Subtract Fractions (Adding & Subtracting Fractions) - Part 1 [11] is a free educational video by Math and Science.

This page not only allows students and teachers view Learn to Subtract Fractions (Adding & Subtracting Fractions) - Part 1 [11] videos but also find engaging Sample Questions, Apps, Pins, Worksheets, Books related to the following topics.