I get it. If a anyone is do this right now, click the upvote.

If I don't get it than do I click downvot?

How do you find a common denomenator for 2 fractions like 1/5 and 2/6?

You would just keep listing all the multiples until you find a common one, so both 5 and 6 are multiples of 30, so the common denominator would be 30

the lowest common denominater of 1/6 and 3/6 is 12 right?

No, in this case 1/6 and 3/6 already have a common denominator of 6.

how do you find the common denominators?

Usually multiple the denominators then cross multiply the denominators by the numerators.So if you have 4/6 x 5/8= what you would do is do 8 x 6 and get 48 thats you products denominator. Then 8 x 4= 32 and 6 x 5= 30. now you have 30/48x32/48=

What's 1/4 plus 11/10?

1∕4 + 11∕10 First, let's find the least common denominator. One way of doing this is to write down multiples of the smaller denominator until we get a number that is also a multiple of the larger denominator. 1 × 4 = 4 (not a multiple of 10) 2 × 4 = 8 (not a multiple of 10) 3 × 4 = 12 (not a multiple of 10) 4 × 4 = 16 (not a multiple of 10) 5 × 4 = 20 = 2 × 10 This tells us that if we multiply 1∕4 by 5∕5 and 11∕10 by 2∕2, the resulting fractions will have the same denominator. 1∕4 + 11∕10 = 5∕5 × 1∕4 + 2∕2 × 11∕10 = (5 × 1)∕(5 × 4) + (2 × 11)∕(2 × 10) = 5∕20 + 22∕20 Now that the two fractions have the same denominator we can simply add the numerators. 5∕20 + 22∕20 = (5 + 22)∕20 = 27∕20

Are two fractions multiplied equals 1 called reciprocals?

Reciprocals are fractions turned upside down and have the numerator in the denominator area with the denominator in the numerator area. For example, reciprocal of 5/8 is 8/5

Main content

5th grade

Course: 5th grade > Unit 4

Lesson 2: Common denominators

Common denominators review

Google Classroom

Review finding common denominators, and try some practice problems.

Common denominators

When fractions have the same denominator, we say they have common denominators.

Having common denominators makes things like comparing, adding, and subtracting fractions easier.

Finding a common denominator

One way to find a common denominator for two (or more!) fractions is to list the multiples of each denominator until we find the smallest multiple they have in common.

Example

Find a common denominator for start fraction, 7, divided by, 8, end fraction and start fraction, 3, divided by, 10, end fraction.

The denominators are 8 and 10. Let's list multiples of each:

Multiples of 8: 8, comma, 16, comma, 24, comma, 32, comma, start color #11accd, 40, end color #11accd, comma, 48, comma, 56, comma, 64, comma, 72, comma, start color #11accd, 80, end color #11accd, point, point, point

Multiples of 10: 10, comma, 20, comma, 30, comma, start color #11accd, 40, end color #11accd, comma, 50, comma, 60, comma, 70, comma, start color #11accd, 80, end color #11accd, comma, 90, comma, 100, point, point, point

start color #11accd, 40, end color #11accd and start color #11accd, 80, end color #11accd are common multiples of 8 and 10. So, we can use either of these for a common denominator. Most often, we will use the smallest common denominator, so we can work with smaller numbers.

Let's use start color #11accd, 40, end color #11accd for our common denominator.

Rewriting fractions with a common denominator

Now, we need to rewrite start fraction, 7, divided by, 8, end fraction and start fraction, 3, divided by, 10, end fraction with a denominator of start color #11accd, 40, end color #11accd.

We need to figure out what to multiply each denominator by to get start color #11accd, 40, end color #11accd:

start fraction, 7, divided by, 8, end fraction, times, start fraction, divided by, 5, end fraction, equals, start fraction, divided by, start color #11accd, 40, end color #11accd, end fraction

start fraction, 3, divided by, 10, end fraction, times, start fraction, divided by, 4, end fraction, equals, start fraction, divided by, start color #11accd, 40, end color #11accd, end fraction

Next, we multiply the numerators by the same number as their denominator:

start fraction, 7, divided by, 8, end fraction, times, start fraction, 5, divided by, 5, end fraction, equals, start fraction, 35, divided by, start color #11accd, 40, end color #11accd, end fraction

start fraction, 3, divided by, 10, end fraction, times, start fraction, 4, divided by, 4, end fraction, equals, start fraction, 12, divided by, start color #11accd, 40, end color #11accd, end fraction

Now we have written start fraction, 7, divided by, 8, end fraction and start fraction, 3, divided by, 10, end fraction with a common denominator:

start fraction, 7, divided by, 8, end fraction, equals, start fraction, 35, divided by, 40, end fraction

start fraction, 3, divided by, 10, end fraction, equals, start fraction, 12, divided by, 40, end fraction

Note: The new fractions are equal to their original form, however they are often easier to work with when the denominators are the same.

Want to learn more about common denominators? Check out this video.

Practice

Problem 1

Current

You have two fractions, start fraction, 2, divided by, 5, end fraction and start fraction, 3, divided by, 10, end fraction, and you want to rewrite them so that they have the same denominator (and whole number numerators).

What number(s) could you use for the denominator?

Want to try more problems like this? Check out this exercise.

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28marianolima
Posted 3 years ago. Direct link to 28marianolima's post “I get it. If a anyone is ...”
I get it. If a anyone is do this right now, click the upvote.
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- ☁︎~ ChloeMac Nuget123 ~☁︎
  Posted 7 months ago. Direct link to ☁︎~ ChloeMac Nuget123 ~☁︎'s post “If I don't get it than do...”
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ml1089
Posted 6 years ago. Direct link to ml1089's post “At first I was really con...”
At first I was really confused with the least common denominator Q's. Then i realised that I had to find the number which was in both multiples. Some questions can be answered like this:

Oh, 3 times 5 is 15! yas

But can you do it another way? (not for the one which you have to times the denominators, but like, the other types of questions)
?/6 and ?/4, something like that. Hope you understand me XD :3
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Jolene
Posted 5 years ago. Direct link to Jolene's post “How do you find a common ...”
How do you find a common denomenator for 2 fractions like 1/5 and 2/6?
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- PuFfY GeMsToNe
  Posted 2 years ago. Direct link to PuFfY GeMsToNe's post “You would just keep listi...”
  You would just keep listing all the multiples until you find a common one, so both 5 and 6 are multiples of 30, so the common denominator would be 30
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how do you find the common denominators?
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- Brayden Davenport
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  Usually multiple the denominators then cross multiply the denominators by the numerators.So if you have 4/6 x 5/8=
  what you would do is do 8 x 6 and get 48 thats you products denominator. Then 8 x 4= 32 and 6 x 5= 30. now you have 30/48x32/48=
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the lowest common denominater of 1/6 and 3/6 is 12 right?
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- Stephen White
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  No, in this case 1/6 and 3/6 already have a common denominator of 6.
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Are two fractions multiplied equals 1 called reciprocals?
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- Aditya Suresh
  Posted 3 years ago. Direct link to Aditya Suresh's post “Reciprocals are fractions...”
  Reciprocals are fractions turned upside down and have the numerator in the denominator area with the denominator in the numerator area. For example, reciprocal of 5/8 is 8/5
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Posted 4 months ago. Direct link to Juliet's post “What's 1/4 plus 11/10?”
What's 1/4 plus 11/10?
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- Jerry Nilsson
  Posted 4 months ago. Direct link to Jerry Nilsson's post “1∕4 + 11∕10 First, let's...”
  1∕4 + 11∕10
  
  First, let's find the least common denominator.
  One way of doing this is to write down multiples of the smaller denominator until we get a number that is also a multiple of the larger denominator.
  1 × 4 = 4 (not a multiple of 10)
  2 × 4 = 8 (not a multiple of 10)
  3 × 4 = 12 (not a multiple of 10)
  4 × 4 = 16 (not a multiple of 10)
  5 × 4 = 20 = 2 × 10
  
  This tells us that if we multiply 1∕4 by 5∕5 and 11∕10 by 2∕2,
  the resulting fractions will have the same denominator.
  
  1∕4 + 11∕10
  = 5∕5 × 1∕4 + 2∕2 × 11∕10
  = (5 × 1)∕(5 × 4) + (2 × 11)∕(2 × 10)
  = 5∕20 + 22∕20
  
  Now that the two fractions have the same denominator we can simply add the numerators.
  
  5∕20 + 22∕20
  = (5 + 22)∕20
  = 27∕20
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