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## MAP Recommended Practice

### Course: MAP Recommended Practice>Unit 34

Lesson 14: Common denominators

# Finding common denominators

Learn all about finding common denominators in fractions. Watch how to use the least common multiple of the denominators to rewrite fractions, making them easier to compare or add. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• How do I find LCM with 3 fractions
• Its quite simple you find out what the three numbers are, lets say the numbers are: 2,3,4.
then you wright the numbers they all have in common.
2: 2,4,6,8,10,12
3: 3,6,9,12
4: 4,8,12
Then circle or look to find witch they all have In common. If you look hard they all have or are equal to the number 12. I hope my answer helped you answer your question :)
• What if one of the denominators is a 1?
• If the denominator is a 1, then it's still the same formula: you simply divide the denominator by the numerator (ex: 4/1 = 4 divided by 1 = 4). It works no matter what the numerator or denominators are, even if the denominator isn't a 1 (ex: 7/3 = 7 divided by 3 = 2 1/3). With 4/1, it's easy to know that it will be 4, but with bigger numbers (ex: 282/47), it can be a lot harder to mentally figure out what your answer will be, so the dividing trick can help a lot in those scenarios. I know this answer is really late -- four years late; sorry -- but I hope either you see this, Noah, or somebody else who needed help sees this and gets the help that they need. :)
• Can someone explane this to me pls?
• So you have to find a common denominator, right? For this one, you have to multiply to get the common denominator. So what times 6 equals 24? Also, what times 8 equals 24? Then that is how you get your common denominator.
• who likes donuts :]
• i do :))
• is LCM n LCD are same?
• The LCM is used to find the LCD but yes they are the same
• What's a common denominator?
• A common denominator is a denominator that you can reach by both denominators. For example in the problem 3/4+ 5/6 a common denominator is 12 because it is the lowest number that both 4 and 6 can reach by multiplying with whole numbers. Thanks for reading hope it helps!
• How to know if you are finding the common denominators with some choices like; 3/4+1/3

A.3/4+1/3 = 9/12+4/12

B.3/4+1/3=9/12+3/12

C.3/4+1/3=12/12+4/12

D.3/4+1/3=3/12+1/12
• The key is to remember that if you multiply the denominator by a value, you also have to multiply the numerator by that same value. In this example, it's clear the common denominator is 12. For the first fraction, to get 12 in the denominator, you have to multiply top and bottom by 3, which gives you 9/12, so this limits your answer choices to A and B. For the second fraction, you have to multiply by 4 on the top and bottom to get 12 in the denominator, so we end up with 4/12. This means our answer is A!
• find the the lcd of 1/5, 1/4 and 1/9?
• Then you can convert it to a mix fraction.