Adding and subtracting fractions
- Adding Fractions with Like Denominators
- Adding fractions with common denominators
- Subtracting Fractions
- Subtracting fractions with common denominators
- Adding and subtracting fractions
- Adding Fractions with Unlike Denominators
- Adding fractions (ex 1)
- Adding fractions
- Subtracting fractions
- Adding and subtracting fractions
Adding Fractions with Unlike Denominators Adding Fractions with Unlike Denominators
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- We're asked to add 4/9 and 11/12 and to write our answer
- as a mixed number, and then simplify and write our answer
- as a mixed number.
- So here we have two fractions we're adding together, but we
- have different denominators.
- So whenever you add fractions, the first thing you have to do
- is check the denominators.
- If they're the same, you can add, but if they're different
- like this, you have to make them have the same
- denominator.
- So what we have to do is find a number that both 9 and 12
- will divide into, and that will be our common
- denominator, and you'll see why both 9 and 12 have to
- divide into it.
- So let's think about what that number is, and there's two
- ways of coming up with that what we could call a least
- common multiple, the smallest multiple of both 9
- and 12 that is common.
- One way is just to kind of look at the multiples of 9 and
- see if any of them are divisible by 12.
- So if you start with 9-- we can do it over here.
- So you have 9, that's not divisible by 12.
- 18 isn't divisible by 12.
- 27 isn't divisible by 12.
- 36, well, that is divisible by 12.
- That is 12 times 3.
- So 9 goes into 36 and 12 goes into 36.
- So what we want to do is write a common denominator.
- So we're going to write 4/9 as something over 36, and we're
- going to write 11/12 as something over 36.
- Now, to turn your 9 into a 36, you have to
- multiply it by 4, right?
- 9 times 4 is equal to 36.
- Now, you can't just multiply the denominator by 4.
- You also have to multiply the numerator by the same thing.
- So if you multiply the numerator by 4, you get 4
- times 4 is 16.
- So 4/9 is the exact same thing as 16/36.
- If you wanted to simplify this one to 4/9, you divide the
- numerator and the denominator by 4.
- Now, we do the same thing over here.
- 36, 12 times 3, so we're multiplying 12 by 3 to get 36.
- Well, if we did that to the denominator, we also have to
- do that to the numerator, so 11 times 3 is 33.
- And just like that, we've now rewritten each of the
- fractions so that they have the same denominator.
- Both of their denominators is 36.
- So now we're ready to add.
- If you add these two things, we'll have 36, because we're
- considering kind of parts of 36 or fractions of 36, and
- then we have 16 plus 33 in the numerator.
- Let me write that down.
- 16 plus 33 in the numerator.
- And 16 plus 33 is what?
- 6 plus 33 would be 39 and then you have
- another 10, so it's 49.
- So it's equal to 49/36.
- Now, can we simplify this?
- 49, it's 7 squared, so it has 1, 7 and 49 as factors.
- This has 1-- it has a bunch of numbers, but it's not
- divisible by 7, so this is actually in simplest form, but
- this is an improper fraction.
- The numerator is larger than the denominator.
- So let's write it as a proper fraction.
- To do that, we divide 36 into 49.
- 36 goes into 49 how many times?
- Well, it only goes one time, so it equals 1.
- And how much will be left over?
- If I divide 36 into 49 one time, or 1 times 36 is 36,
- then I have 13 left over to get to 49.
- So it's 1 and 13/36.
- And you can do that manually, if you like you.
- You'd say 36 into 49.
- 36 goes into 49 one time.
- 1 times 36 is 36, and then you subtract.
- 9 minus 6 is 3.
- 4 minus 3 is 1.
- You have a remainder of 13.
- So that's our answer: 1 and 13/36.
why does the denominator have to be the same as the other denominator
gmorgenegg
Because when you add or subtract you only add or subtract the numerator, and not the denominator. If you have a different denominator for each fraction, say you had 3/4 + 18,
you can, not, add the denominator AND numerator, because if you do, you get 6/12, which is the wrong answer and if that was the way we added fractions it would be way too easy.
So you need to find the common denominator, by listing the two denominators for each fraction:
4:
8:
then writing out the multiples,
4: 4, 8,
8: 8,
then once you find a common multiple, that common multiple becomes the denominator:
3/8 + 1/8
And since you changed the denominator for one of the fractions, you change the numerator for that fraction, according to the difference for what that fraction's denominator used to be, to what it now is:
3/4 -> 3/8
4 x 2= 8
So then you do that change to the numerator to even it out:
In 3/4, the numerator is= 3
So you do 3 x 2, which equals 6, so your new fraction and numerator is 6/8.
Now you have 6/8+1/8, and since you ONLY add the numerator, you get 7/8 for your answer.
you can, not, add the denominator AND numerator, because if you do, you get 6/12, which is the wrong answer and if that was the way we added fractions it would be way too easy.
So you need to find the common denominator, by listing the two denominators for each fraction:
4:
8:
then writing out the multiples,
4: 4, 8,
8: 8,
then once you find a common multiple, that common multiple becomes the denominator:
3/8 + 1/8
And since you changed the denominator for one of the fractions, you change the numerator for that fraction, according to the difference for what that fraction's denominator used to be, to what it now is:
3/4 -> 3/8
4 x 2= 8
So then you do that change to the numerator to even it out:
In 3/4, the numerator is= 3
So you do 3 x 2, which equals 6, so your new fraction and numerator is 6/8.
Now you have 6/8+1/8, and since you ONLY add the numerator, you get 7/8 for your answer.
Alexandra
Aaron Berlin Murphy
IsaiahMath
Ms. E (Epic)
zach.hansen
JEFFREY LAY
What does it mean to simplify the problem?
Dan
Simplifying is just making the fraction smaller
Lauren
Isaac Fingerson
Meg Simmons
what if the denominators of two fractions don't have a least common multiple, like in 3/10 + 3/7? What do you do? Please help!
You mean, they don't have a greatest common divisor?
Then you have to simplify them, but in this case it's not possible.
Then you have to multiply them inself, so you get the least common multiple LCM(10,7)=70.
3/10 => 21/70
3/7 => 30/70
Then you have to simplify them, but in this case it's not possible.
Then you have to multiply them inself, so you get the least common multiple LCM(10,7)=70.
3/10 => 21/70
3/7 => 30/70
SophieMonte
jnwang03
its soooo confusing what is he trying to explain!
he is trying to explian the important concept of learning the chapter of hard math
Why did people make Fractions its just so CONFUSING!
Fractions can be confusing, but they are a great way to represent a part of a whole.
when im adding uncommon fractions, i keep getting it wrong. what im saying is i dont understand. please tell me the steps.
Neilie
Well it has to equal 1.So say 2/4 and 4/6 jbj;sgkdxf
what is he trying to say? it is confusing.
Well not really if your getting this then why do you need the video? But if your having lots of trouble and you NEED help then you can go on youtube but it depends if you know the concept or not to answer your question
benandersonflint
how do i add fractions ?
because you can who got some to say about that
3/4 + 1/2=answer in simplest terms
In order to add fractions, the denominators must be the same.
The lowest common denominator or multiple (LCD or LCM) is 4.
Whatever we multiply the denominator by, we must multiply the numerator by.
Therefore, 1/2 = 2/4.
So, 3/4 + 2/4 = 5/4 as an improper fraction or as 1 1/4 as a mixed number.
The lowest common denominator or multiple (LCD or LCM) is 4.
Whatever we multiply the denominator by, we must multiply the numerator by.
Therefore, 1/2 = 2/4.
So, 3/4 + 2/4 = 5/4 as an improper fraction or as 1 1/4 as a mixed number.
Why do the denominators have to be the same?
Because the denominator of a fraction can be thought of as a unit and when adding values they have to have the same unit. You can't add inches and centimeters without converting them to the same unit.
how do you add a mixed number with an fraction for example 4 2/3 + 1/6
Now it would be 4 5/6.
what is 4 2/3 + 1/6
This can't be a homework question though since other people are asking the same thing...
what about if the denominators are 4 and 5
Then you need to find a way to make them the same. So if you multiply 4 times five and 5 times four you get 20, and then both denominators are the same.
Just make sure you remember to multiply the numerators too. :)
Just make sure you remember to multiply the numerators too. :)
I don't get this it is hard can anybody help me?
For adding fractions with unlike denominators, you would need to change the numbers below the bar (denominators) by finding the least common factor/multiple.
Example:
3/4 + 3/16
Convert 3/4 to sixteenths.
4 (4) is 16
3 (4) is 12
Both numerators have to be multiplied by the same numbers.
12/16 + 3/16 = 15/16
Hope this helps!
Example:
3/4 + 3/16
Convert 3/4 to sixteenths.
4 (4) is 16
3 (4) is 12
Both numerators have to be multiplied by the same numbers.
12/16 + 3/16 = 15/16
Hope this helps!
how do you subtract a broblem
You first use the same method as shown in this video to find common denominators.
Once the denominators are alike, the fractions can be added or subtracted.
Here is a video on "Adding and Subtracting fractions" with like denominators.
http://www.khanacademy.org/math/arithmetic/fractions/Adding_and_subtracting_fractions/v/adding-and-subtracting-fractions
Once the denominators are alike, the fractions can be added or subtracted.
Here is a video on "Adding and Subtracting fractions" with like denominators.
http://www.khanacademy.org/math/arithmetic/fractions/Adding_and_subtracting_fractions/v/adding-and-subtracting-fractions
thanks Sal helped me with my homework
yah he is really good. you can tell he did his homework:)
Sal gets the answer 49/36 which is 1 13/36.If I take the square root of both the numerator and denominator I get 7/6 which is 1 1/6. Isn't taking the square root of the denominator and numerator a valid operation?
What if both numbers don't have a greatest common factor?
William Walton
Hi William. Two numbers always have a greatest common factor. Sometimes, it is 1, but often it is larger.
i think you can also just multiply the denominaters by each other........right?
That works. You may have to multiply larger numbers, though...
This website has helped me a lot in my school work. Although i am a little confuzzled on how he got his answer, like how did he turn it to a mixed #?
First he used LCM to get 36. So he did 9x4(36), which meant he had to do 4x4(16). Then he did 12x3(36), which meant he did 11x3(33). For fractions, he did 36+36=36(I know, it probably doesn't make any sense but its true) and then 16+33(49). 36 only goes into 49 once, with a remainder of 13 so he got 1 and 13/36. I hope that helped, Mikayla!
why does the denominator have to be the same?
The denominator has to be the same because then it makes it easier to add, subtract, multiply, or divide the fraction.
If you have a prime number as a denominater and a composite number as a denominater. What do you do if the prime number doesn't go into the composite number?
read my question, I think it will help. here-
A tip from the math freak- the two denominators in a problem can be multiplied by each other to find the common denominator.
Take this example: this is how I would do a problem like this-
8/12 + 4/13 = ?
Multiply 12 and 13 to find the common denominator. {156}
Then, multiply the 13 by 8 to get the numerator to be the same. 104/156
Then, multiply the 12 by 4 to get the numerator to the other fraction. 48/156
Do the problem, then simplify simplify simplify.
A tip from the math freak- the two denominators in a problem can be multiplied by each other to find the common denominator.
Take this example: this is how I would do a problem like this-
8/12 + 4/13 = ?
Multiply 12 and 13 to find the common denominator. {156}
Then, multiply the 13 by 8 to get the numerator to be the same. 104/156
Then, multiply the 12 by 4 to get the numerator to the other fraction. 48/156
Do the problem, then simplify simplify simplify.
can you please teach me calculus ?
That's in the calculus section.
I don't really understand how to simplify. It is confusing to me somehow and everytime I get a question that asks me to simplify I can't do it, I don't understand it. Can somebody please help me figure it out?
wat questions do you need help with
If there is no common denominator(except for multiplying the two numbers, of course.)
does it have to be the product of the two numbers?
does it have to be the product of the two numbers?
thanks, whats your name,? is it sal
Yes it is Sal Khan
Anais
Would 1 39/108 be an acceptable answer?
Also, is 1 39/108 equal to 1 13/36?
Also, is 1 39/108 equal to 1 13/36?
1 39/108 *does* equal 1 13/36.
and, It is preferred to have 1 13/36 over 1 39/108.
and, It is preferred to have 1 13/36 over 1 39/108.
Can some one please tell me where I can practice this skill. I can not find the practice page that goes with this?
when your school starts ask your teacher for a paper or go on google and say blah blah blah and the print
how do i write 2 to the power of something?
Just write the number 2, which is the base, then put in whatever exponent you want.
Is there a name for the answer you get when you add/subtract fractions?
10,020,396 over 300,285,932 plus 125 over 70,000,000. Seems hard. bet you I can fool ya. :)
Is there a practice section for adding fraction with unlike Denominator?
There probably is, and you can check the Knowledge Map, but I don't really know for sure.
How do you add a fraction and a whole number? Like 34 + 23/12?
Why would you multiply 34x12/1x12? Wouldn't that still just be 34?
hey dont all u do is find the LCD and then add them up? u dont have to do all that fancy stuff? not for 4:26. it will take about 1 min for me. im not in tag if people respond im just learning this on my own. RESPOND ASAP
i just dont get how you simply the fraction please help me
To simplify a fraction, you divide the numerator and denominator by the same numbers until you can no longer divide both the top and bottom by the same number. For example: 4/8 divide the top by 4 and the bottom by 4 and you get 1/2. 1/2 is a simplified fraction.
How do you add something like this: -5/(x-7)+12/(x+6) ? If you could do a video on how to do that, it would be much appreciated. Thanks
Why do u have to multiply in Fractions? In unlike denominator fractions?
i don't know how to make the fraction simple
Find the lowest multiple of both numbers
i thought that you had to add the different denominators but you have to divide them
so when your multiplying do you have to divide the different denominators and so when your dividing different denominators you have to multiply them
so when your multiplying do you have to divide the different denominators and so when your dividing different denominators you have to multiply them
why the same number?
It has the same number more than once....why?
Can you please make a video on simplifying fractions? That is what I am struggling with.
Okay so this is today's homework is about that and I haven't really get what I had to do so look at this problem 1/3 + 5/9 they both can't reduce! or unless you can do the factor tree on 1 and 3 okay never mind thank you for doing this video I really didn't understand Adding Fractions with Unlike Denominators. and plus is their ever gonna be a problem with dividing? Like with unlike denominators?
To add fractions, find the least common denominator (LCD). Here, it would be 9.
1) You can convert 1/3 to 3/9. So you end up with 1/3 + 5/9 = 3/9 + 5/9.
2) Add the numerators. (3+5)/9 = 8/9.
1) You can convert 1/3 to 3/9. So you end up with 1/3 + 5/9 = 3/9 + 5/9.
2) Add the numerators. (3+5)/9 = 8/9.
Michael Dumont
WHat about three different fractions?? My book isn't helping me at all, I thought I had it but I keep getting it wrong..
I have watched this vidro a hundred times and I still dont get how to add unlike fractions please help!
On every video, they use easy problems, how come they dont use hard ones. It would make this a lot easier. :)
hi this is family5515<3 here do any of u know a more easy way to do this?
if u do plz message me thx
Can u multiply it with a bigger denominater ?
Sure, you can use any denominator you want, as long as they are common. Then reduce at the end for the last step. Tip: See the recognizing divisibility video. It is very helpful.
What if both denominators are prime numbers? Such as 9/13 + 7/11 how would I do it then?
Any help is most welcome.
Any help is most welcome.
if they are prime then you obviously cant simplify
*BUT*
you can find the LCM which in your example is *143*
see this video: http://www.khanacademy.org/math/arithmetic/fractions/v/finding-common-denominators
to understand better
*BUT*
you can find the LCM which in your example is *143*
see this video: http://www.khanacademy.org/math/arithmetic/fractions/v/finding-common-denominators
to understand better
how about if we have like 36, and we have to find a GCF, and we have to do 2. what can save me from doin all that work?
i dont know but good question.
Make a video that tells me how to simplify a fraction that is NOT an improper fraction!
thanks so much, now i can understand it much better! I just wanted to ask, what if one of the denominaters is a prime number?
How do you reduce
Try finding numbers that go into both numbers.
24 and 9 are both divisible by 3 so if a fraction looked like
9/24
you could reduce it to
3/8
24 and 9 are both divisible by 3 so if a fraction looked like
9/24
you could reduce it to
3/8
This looks hard can some one help?
Thank's! I got it down now !
is it true sal has other subject besides math i just started so i dont no munch about kwan acamdy ;0
hello need math HELP i need to subtract mixted numbers with UN common denominators here
12 5/8 -3 3/4
get back quick plz
12 5/8 -3 3/4
get back quick plz
is there adding and subtracting negative fractions with unlike denominators?????i need feedback
yes find it
Do you know about any short cuts to make it go faster? Sometimes I find myself going really slow.
I am lost. can someone explain when you need to simplify the fraction at the beginning or the at the end of the problem?
How would you do M over (2m+3) + M over (m+3) ?
I think what your trying to say has something to do with equations. If you're having trouble on that problem, sheck out the equations.
Can you do cross multiplying? My mom says i can but my older sister says no?
is there any videos on subtracting fractions with different denominators
I was trying to watch Adding fractions with like denominators so I hit watch on the videos page but it brought me to this video - Adding fractions with unlike denominators. WHY???
It comes up in the questions... It helps just to do it all at once.
please help! what do you do if a fraction has x in the denominator?? for example 1/2x + 4/5x =??
thank you i get it now
i am not trying to be mean but thats a comment:)
I still don't understand this...I don't want to make it back up to a mixed. Is there any videos that show how to add unlike denominators that becomes improper or proper fraction?
Rub
i think the questions are to hard my mom yes because 2+2=4 but it said it was 5 my mom my mom my mom my mom yes
Why are both the denominators the same?
If you want to add or subtract a fraction, you have to make both side have the same denominator.
this was awesome! Now i can do another thing in my Kahn Academy project.
If you have a prime number as a denominater and a composite number as a denominater. What do you do if the prime number doesn't go into the composite number?
Multiply the prime by the composite and that can be used as your common denominator
If you are adding fractions with unlike denominators and you have a variable in the equation, do you multiply the variable inorder to create a common denominator like the fractions in the equation?
when you turn a mixed fractions into a proper fraction,you know 49 goes into 36 once and so can't you do 49-36=13?
hi this was REALY helpfull thnx!
yea ur rite..... XD
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