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Adding fractions with unlike denominators

Adding Fractions with Unlike Denominators

Adding fractions with unlike denominators

Discussion and questions for this video
why does the denominator have to be the same as the other denominator
Good question.
In mathematics, the concept of adding and subtracting fractions require the denominator to be common. The numerator does not need to be common but the denominator must be.
If the denominator wasn't common how would we work out the question?
E.g. 1/3 + 3/7 = ?
To work out this question, we would have to find the LCM (Lowest Common Multiple) of the denominators; in this case, 3 and 7. Then when we find that it is 21, we can adjust the numerators to 7 and 9. With that done, we can add 3 and 7 to make 10 over the denominator, which is 21.

This is why the denominators have to be common. There was no equation or formula built in the concept of adding and subtracting fractions that do not require the denominators to be common.

I hope this clears everything up. :)
Why did he say to turn the nine in to a 36 and why multiply by 4 what.]
nine times four is thirty six but why cant the nine just be nine. I'm confused ):
and why do we have to multiply the numerator by 4 too.~_~
to add fractions, you need to have the denominator the same. these two fractions have denominators of 9 and 12. The lowest common multiple of these two numbers is 36. That requires multiplying by x4 and x3 respectively. We multiply the numerator and denominator by the same number so the number does not change.
4/9 * 4/4 = 16/36. 4/4 is the same as 1, so the number doesn't change
If both denominators are prime numbers, is the only least common multiple between them always going to be the product of the two?
Well, yes because since both are prime numbers, and prime numbers can't divide into each other's multiples, it will have to be the product. For example, 1/5 + 1/7, 7 can't divide into 5's multiples and 5 can't divide into 7's multiples, so the denominator has to be the product. By the way the answer is 7/35 + 5/35 = 12/35
Why do the denominators have to be the same?
You do not have to make them the same but it makes it far easier to do.
why does the denominater have to be greater than the top number?
Excellent question my friend. If you had two fractions like 6/5 and 7/5 you would get 13/5. That is what you would call a improper fraction. In arithmetic you wouldn't leave it like that because it's considered a improper fraction. You would need to change it into a mixed number. When you get to algebra 1 they will allow you to leave it as a improper fraction as an answer to a problem.
I don't get this it is hard can anybody help me?
it is quite simple if you ask me all you have do is this Whenever you add fractions with unlike denominators, you must make the denominators of the same value. In this example, the easiest approach is to multiply 8 x 3 to get 24. Here, you multiply by 3 to get . Then you multiply the second equation by 8 to get . Note that both addends have 24 as a denominator. Add in the same manner as with the unit Adding fractions with like denominators.
can you divide fractions
yes you can beacuse fractions are the answer of 1 divide by a number so yes they can
i cant understand this, how did you get the x3 but the other x4?
Because it is a fraction you can multiply it by anything - it will still be the same fraction of a whole number. (1/2 * 2 is 2/4 - but both are 0.5 in decimal terms)

The objective is to get the denominators the same.
can both fractions be negativs
check the number line. can you add two negative numbers? the answer is yes.
Is multiplying a fraction as easy as adding and subtracting one?
Multiplying is even easier because you don't have to find any common denominators or anything. You just multiply across: the numerator times the numerator and the denominator times the denominator.
What if you have a problem where one of the fractions has to be divided into a fraction, and the other number is whole?
If one number is whole, you put it over a denominator of 1. If you have 24/8 - 2, write:
24/8 - 2/1
Hope this helps!
I still don't understand. Please help me i have test next week.
Well when you add a fraction like 4/6 and 9/10 you have to get a common denominator. To do that multiply the denominator 6x10= 60 now the fraction would look like _/60 all we need to do is fine the numerator 6x what = 60 its 10 then we do 10x4 to get the numerator 40/60 do the same thing to the other one now we got 54/60 + 40/60 ok add the numarator 54+40=94 so now we got 94/60 we need t turn it into a mixed number. How much times can 94 go into 60 its 1 time so now we have 1 and 34/60 and thats not your answer yet you have to reduce. So divided by 2 = 17 then 60 divided by 2 is 30 so 17/30.
What if the Denominator was different from the other Denominator?

That's what were talking about here. "Unlike Denominators" are fractions with- literally- Unlike denominators.
Try the Skill "Adding Fractions" when you're done!
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.
what if there was an x in the denominator like in the problem 1/x + 4/1
That is a more advanced type of problem, but you can still find a common denominator.
you could multiply 4/1 by x/x and get 4x/x
then add the numerators 1 + 4x, which can't be simplified further.
So the new form is the (1 + 4x)/x also written as

1 + 4x

This isn't really any simpler than the previous expression but they are equal.
What if both numbers don't have a greatest common factor?
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?
yes, you can just multiply the denominators by each other, but when you use larger numbers, it becomes tedious to multiply all of those giant numbers. It is much simpler to work with smaller numbers, and you are less likely to make a mistake that way. Multiplying the two numbers together is sometimes the only way to get a common denominator.
do you have fractions with multiplication
Yes they do have fractions with multiplication khan academy.
we are doing this in math and i kinda understand it but its hard also
Agreed, I still think fractions is a pain in the neck, but just work hard and you'll understand it.
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 #?
thank you so much! I have a test soon on this so u were just in time ^-^ thanks again
I do not get the mixed fractions, is there an easier way
What don't you understand about them?
what is he trying to say? it is confusing.
it is, why doesn't it have audio
When numerator is greater than the denominator.. it is considered as improper fraction?
Yes it is a improper fraction so you need to turn it into a mixed number.
what if the denominators of two fractions don't have a least common multiple
you work with them in the way as they are - they are already simplified ;)
i don't know how to make the fraction simple
why is this so hard i kinda understand but not really who agrees
I usually forget how to add them does anybody have any tips for me?
natasha had sevon eighth gallon of paint.Her brother ivan took one fourth gallon to paint his model boat. Natasha needs at least one half gallon to paint her bookshelf. Did ivan leave her enough paint.
What thingy are you doing the thing. And are you Indian I'm Indian.
You need to do the LCD if your Denominator is different at Adding Fractions.
Thanks for the video but I was sort of confused with how you got the 3.
When I search for hint. It does not seems well And i Gotta do my math right now. BYE EVERYONE
Why would you not simplify this answer, 22/21 to 1 1/21?
The problem was 5/7 + 1/3. In my homework book it said the answer was simply 22/21.
I'm puzzled...someone please explain!
how did you know to multiply in the begging of the video
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
why do you have to have the sam e denominator
the denominator of a fraction is its place value and the numerator is the digit .
when we add we must add digits with the same place value.
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?
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?
It doesn't matter: Say you have 3/5 + 4/7. They're prime, but the LCM, as you can see, is 35. 5*7=35, 7*5=35. And you probably know how to add them from there.
i dont get it why does the denominator have to be the same as the other denominator? (:
what if the numerator does not go in to the number that denominator does
How would you do M over (2m+3) + M over (m+3) ?
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
i still dont get nothing by the way dont put my question at the bottom
If the denominator of both numbers are prime then why can't 1 be divisible by that prime number?
10,020,396 over 300,285,932 plus 125 over 70,000,000. Seems hard. bet you I can fool ya. :)
I don't get how you did the numbers 9 18 and 27 were wrong yet 36 was right, Can you help me out?
the whole thing was confusing
you cant answer that it dosent make sense fractions only
is there adding and subtracting negative fractions with unlike denominators?????i need feedback
Why do we have to find a common multiple? Why cant we just the numerators and the denominators together, like we multiply the numerators and the denominators when we are multiplying fractions. I'm confused. Help!

I don't understand. This just confuses me. Can anyone turn this video into something that a 13 yr. old can understand?
well me too, but I'll be 13 next month. Well, we'll have to understand it sooner or later...
this video has helped me like sooooooooo much. THANKS SAL!
no prob!!!!!!!!!!!!!!
Do you know about any short cuts to make it go faster? Sometimes I find myself going really slow.
How do you simplify it if it is not an improper fraction?
But what if you get a improper fraction do you have to turn it into a mixed number or can you just let it be.
If your asked to "simplify" the answer, turn it into an improper fraction. Other than that, it depends on whether or not your teacher wants you to.
vote-if u agree that the person who made this website is trying to turn the unlike denominator into a common denominator to make it more easier
why do you have to multiply by the same number
You have to multiply the same number for the denominator and numerator because whatever you do to the bottom, you do to the top. If you don't do this your fraction would not be equivalent so you would get a different answer because you changed the value of the fraction completely. Hope this helped. :)
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?
is there also ever gonna be a unequal problem?
What if both denominators are prime numbers? Such as 9/13 + 7/11 how would I do it then?
Any help is most welcome.
if they are prime then you obviously cant simplify
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
What if i have two denominators that don't divide into any number equally, like nine and eleven?
Why does the numorator have to be on the top and the denominator have
to be on the bottom?
u are soo smart.. just what i need to no except can you do a vidio were you can like turn the inproper fraction into a proper one?? if that makes sence
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?
please help! what do you do if a fraction has x in the denominator?? for example 1/2x + 4/5x =??
is there any way to do it without changing the denominators?
Are decimals the same as fractions? If so, how would you add and subtract it? Would you have to go through the process of all that Sal said you should do?
how to find a common multiple?
Why is this so difficult?
If you work harder, it will be easier.
Is LCM the only way to add fractions with unlike denominators?
Hi, I was wondering if you were going make 49/36 into a proper fraction like he did... it there any other possible way of doing that? Or is that the only way to covert the improper fraction into a proper fraction? Just wondering! Thanks!
what if the numerator to the first fraction is smaller than the second fraction's numerator and you are subtracting.
If that's the case, you'll end up with a negative fraction.
Is it possible for there to not be a common denominator ?
I don't get why we have to multiply
I thought you have to divide 36 to 4/9 and to 11/12 ???
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.
this was awesome! Now i can do another thing in my Kahn Academy project.
Is there another way that you can do this process?
what should i do if my fraction is 9/11+6/10
How do you add fractions with unlike fractions can anyone give me some steps
is their a easer way to make the denominator the same
can you please show hard and not easy like 9 and 12 ha s denominator and some thing like 7 and 8
how do u add and subtracted fractions
instead of listing the factor could you just multiply them please respond :D
why do the fractions have to be simplified?
It is so you can show it in a simplest form and when it comes to percents it will come in handy. From Me
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.
Srry but i still dont get it and dose not work
hi i really dont get adding fraction like i wonder if u can help me
Why do we have covert mixed numbers to improper fractions?
What I don't get is 36/49= 0.7... I have to make it 1? And if it was 0.5?
why do u need to do a common denominator
Can u write a fraction like this -5/9?
Report a mistake in the video

At 2:33, Sal said "single bonds" but meant "covalent bonds."

Report a mistake in the video

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