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=

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

4th grade

Course: 4th grade > Unit 7

Lesson 2: Common denominators

Common denominators review

CCSS.Math:

4.NF.A.2

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.

Want to join the conversation?

Sort by:

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.
Button navigates to signup pageComment on 28marianolima's post “I get it. If a anyone is ...”
(286 votes)
Answer
- ☁︎~ ChloeMac Nuget123 ~☁︎
  Posted 3 months ago. Direct link to ☁︎~ ChloeMac Nuget123 ~☁︎'s post “If I don't get it than do...”
  If I don't get it than do I click downvot?
  Comment on ☁︎~ ChloeMac Nuget123 ~☁︎'s post “If I don't get it than do...”
  (25 votes)
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
Button navigates to signup pageComment on ml1089's post “At first I was really con...”
(87 votes)
Answer
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?
Button navigates to signup pageComment on Jolene's post “How do you find a common ...”
(40 votes)
Answer
- 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
  Comment on PuFfY GeMsToNe's post “You would just keep listi...”
  (16 votes)
ahumphries5266
Posted 3 years ago. Direct link to ahumphries5266's post “That was sorta hard but f...”
That was sorta hard but fun
Button navigates to signup pageComment on ahumphries5266's post “That was sorta hard but f...”
(26 votes)
Answer
- BLAKEM
  Posted 4 months ago. Direct link to BLAKEM's post “Can you up vote this”
  Can you up vote this
  Comment on BLAKEM's post “Can you up vote this”
  (14 votes)
Mariana Olivares
Posted 4 years ago. Direct link to Mariana Olivares's post “how do you find the commo...”
how do you find the common denominators?
Button navigates to signup pageComment on Mariana Olivares's post “how do you find the commo...”
(6 votes)
Answer
- Brayden Davenport
  Posted 3 years ago. Direct link to Brayden Davenport's post “Usually multiple the deno...”
  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=
  Comment on Brayden Davenport's post “Usually multiple the deno...”
  (17 votes)
Aeriunna Ty'kedria Strong
Posted 4 years ago. Direct link to Aeriunna Ty'kedria Strong's post “If you don't understand j...”
If you don't understand just ask the teacher! 😘
Button navigates to signup pageComment on Aeriunna Ty'kedria Strong's post “If you don't understand j...”
(15 votes)
Answer
- gabriel.oli.ren
  Posted 2 years ago. Direct link to gabriel.oli.ren's post “I don't have a teacher I ...”
  I don't have a teacher I have a tutor
  Comment on gabriel.oli.ren's post “I don't have a teacher I ...”
  (0 votes)
$male robot johnny style avatar for user /-/@\^/E0$
/-/@\^/E0
Posted 4 years ago. Direct link to /-/@\^/E0's post “the lowest common denomin...”
the lowest common denominater of 1/6 and 3/6 is 12 right?
Button navigates to signup pageComment on /-/@\^/E0's post “the lowest common denomin...”
(8 votes)
Answer
- Stephen White
  Posted 4 years ago. Direct link to Stephen White's post “No, in this case 1/6 and ...”
  No, in this case 1/6 and 3/6 already have a common denominator of 6.
  Comment on Stephen White's post “No, in this case 1/6 and ...”
  (14 votes)
EEJ
Posted 5 years ago. Direct link to EEJ's post “Are two fractions multipl...”
Are two fractions multiplied equals 1 called reciprocals?
Button navigates to signup pageComment on EEJ's post “Are two fractions multipl...”
(2 votes)
Answer
- 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
  Comment on Aditya Suresh's post “Reciprocals are fractions...”
  (14 votes)
˗ˏˋ Bella ´ˎ˗
Posted 18 days ago. Direct link to ˗ˏˋ Bella ´ˎ˗'s post “:3 ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣤⡤⠤⠤⠤...”
:3 ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣤⡤⠤⠤⠤⣤⣄⣀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⡤⠞⠋⠁⠀⠀⠀⠀⠀⠀⠀⠉⠛⢦⣤⠶⠦⣤⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ ⠀⠀⠀⠀⠀⠀⠀⢀⣴⠞⢋⡽⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠃⠀⠀⠙⢶⣄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ ⠀⠀⠀⠀⠀⠀⣰⠟⠁⠀⠘⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢰⡀⠀⠀⠉⠓⠦⣤⣤⣤⣤⣤⣤⣄⣀⠀⠀⠀ ⠀⠀⠀⠀⣠⠞⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣴⣷⡄⠀⠀⢻⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠻⣆⠀ ⠀⠀⣠⠞⠁⠀⠀⣀⣠⣏⡀⠀⢠⣶⣄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠹⠿⡃⠀⠀⠀⣧⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠸⡆ ⢀⡞⠁⠀⣠⠶⠛⠉⠉⠉⠙⢦⡸⣿⡿⠀⠀⠀⡄⢀⣀⣀⡶⠀⠀⠀⢀⡄⣀⠀⣢⠟⢦⣀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣸⠃ ⡞⠀⠀⠸⠁⠀⠀⠀⠀⠀⠀⠀⢳⢀⣠⠀⠀⠀⠉⠉⠀⠀⣀⠀⠀⠀⢀⣠⡴⠞⠁⠀⠀⠈⠓⠦⣄⣀⠀⠀⠀⠀⣀⣤⠞⠁⠀ ⣧⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣼⠀⠁⠀⢀⣀⣀⡴⠋⢻⡉⠙⠾⡟⢿⣅⠀⠀⠀⠀⠀⠀⠀⠀⠀⠉⠉⠙⠛⠉⠉⠀⠀⠀⠀ ⠘⣦⡀⠀⠀⠀⠀⠀⠀⣀⣤⠞⢉⣹⣯⣍⣿⠉⠟⠀⠀⣸⠳⣄⡀⠀⠀⠙⢧⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ ⠀⠈⠙⠒⠒⠒⠒⠚⠋⠁⠀⡴⠋⢀⡀⢠
Button navigates to signup pageComment on ˗ˏˋ Bella ´ˎ˗'s post “:3 ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣤⡤⠤⠤⠤...”
(13 votes)
Answer
- Bailey<3
  Posted 17 days ago. Direct link to Bailey<3's post “⠈⠉⠉⠈⠈⠈⠉⠉⠉⠉⠉⠉⠉⠉⠙⠻⣄⠉⠉⠉⠉⠀⠀⠀⠀...”
  ⠈⠉⠉⠈⠈⠈⠉⠉⠉⠉⠉⠉⠉⠉⠙⠻⣄⠉⠉⠉⠉⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠓⣄⠀⠀⢀⠀⢀⣀⣤⠄⠀⠀⠀⠀⠀⠀⠀
  ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⢷⣉⣩⣤⠴⠶⠶⠒⠛⠛⠀⠀⠀⠀⠀
  ⠀⠀⠀⠀⠀⠀⠀⠀⣴⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⣧⠤⠶⠒⠚⠋⠉⠀⠀⠀⠀⠀⠀⠀
  ⠀⠀⠀⠀⠀⠀⢀⣾⡍⠀⠀⠀⠀⠀⠀⠀⠀⢠⣾⣫⣭⣷⠶⢶⣤⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠸⣆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠶⠶⠖⠚⠛⠛⣹⠏⠀⠀⠀⠀⠀⠀⠀⠀⠴⠛⠛⠉⡁⠀⠀⠙⠻⣿⣷⣄⡀⠀⠀⠀⠀⠀⠀⠀⠀⢹⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⠀⠀⠀⠀⢠⡏⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⡷⠷⢿⣦⣤⣈⡙⢿⣿⢆⣴⣤⡄⠀⠀⠀⠀⢸⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⠀⣠⣤⡀⣸⡄⠀⠀⠀⠀⠀⠀⠀⢀⣤⣿⣿⣟⣩⣤⣴⣤⣌⣿⣿⣿⣦⣹⣿⢁⣿⣿⣄⣀⡀⠀⢸⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⢠⣿⠋⠻⢿⡁⠀⠀⠀⠀⠀⠀⠀⠀⢸⡿⠿⠛⢦⣽⣿⣿⢻⣿⣿⣿⣿⠋⠁⠘⣿⣿⣿⣿⣿⣿⣼⣧⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⢸⣿⠁⠀⠀⠙⠆⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠒⠿⣿⣯⣼⣿⡿⠟⠃⠀⠀⠀⣿⣿⣿⣿⣿⡛⣿⡟⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
  ⠀⢸⣧⣴⣿⡟⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣺⠟⠃⠀⠀⠀⠀⠀⠀⠙⣿⣿⣿⣿⣿⣿⢁⣀⣀⣀⣀⣀⣠⣀⣀⢀⢀⢀
  ⠀⠀⢿⠿⣿⡄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⡆⠙⠛⠛⠙⢻⣶⣶⣾⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⣿⣿⡇⠀⠘⠃⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⡞⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⡟⢿⣿⣆⠀⣸⠇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢄⡼⠁⢀⣀⡀⠀⠀⠀⣦⣄⠀⣠⡄⣸⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⣷⣬⢻⣿⡿⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⣧⣰⣿⡿⠿⠦⢤⣴⣿⣿⣷⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⣿⣿⣸⣿⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠛⠛⠛⠒⣿⣿⣿⡿⠟⠹⣼⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⣿⠸⣿⣿⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣿⣿⣿⡖⠀⢠⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⡿⣾⣿⣸⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣆⣀⣀⣤⣴⣶⣶⣾⣿⣷⣦⣴⣼⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⡇⣿⣿⡛⡇⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣠⢾⡟⠛⠛⠻⠛⠛⠛⠿⠿⠿⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⠓⢁⣬⣿⠇⠀⠀⠀⠀⠀⢠⡀⠀⠀⠀⠀⠀⢰⡿⣻⠇⠀⠀⠀⠀⠀⣠⣶⣶⣶⣶⣿⣿⡿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⢐⣯⠞⠁⠀⠀⠀⠀⠀⠀⣄⠱⣄⠀⠀⠀⠀⠸⡧⠟⠆⠀⠀⠀⠀⠘⠿⢿⠿⠿⣿⡿⣿⠃⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⡾⠃⠀⠀⠀⠀⠀⠀⠀⠀⠘⢦⡈⠂⠀⠑⢄⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⢠⣿⠀⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠈⠒⡄⠀⠀⠑⠄⠀⠀⠀⠀⠀⠀⠀⢀⣠⣤⣦⣦⣼⡏⠳⣜⢿⠻⢿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠁⠀⠀⠀⢠⣷⣦⣤⣀⣀⣀⣴⣿⣿⣿⣿⣿⡿⠻⠆⠸⣎⣧⠀⠈⠙⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿
  ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣄⠀⠀⠀⣸⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠁⣠⡄⠀⣿⢹⡇⢸⡀⠀⠈⠻⢿⣿⣿⣿⣿⣿⣿
  Comment on Bailey<3's post “⠈⠉⠉⠈⠈⠈⠉⠉⠉⠉⠉⠉⠉⠉⠙⠻⣄⠉⠉⠉⠉⠀⠀⠀⠀...”
  (1 vote)
tshapter_s
Posted 6 years ago. Direct link to tshapter_s's post “the secend last q on prac...”
the secend last q on practice dose not work
Button navigates to signup pageComment on tshapter_s's post “the secend last q on prac...”
(8 votes)
Answer