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Course: Grade 5 math (FL B.E.S.T.) > Unit 4
Lesson 2: Common denominatorsCommon denominators review
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 and .
The denominators are and . Let's list multiples of each:
Multiples of :
Multiples of :
Let's use for our common denominator.
Rewriting fractions with a common denominator
Now, we need to rewrite and with a denominator of .
We need to figure out what to multiply each denominator by to get :
Next, we multiply the numerators by the same number as their denominator:
Now we have written and with a common denominator:
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.
Want to join the conversation?
- 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(128 votes)- At first i was confused by the option 15 because i wasn't thinking straight and thought that 15 was 10 times five instead of 10 plus five :)(18 votes)
- How do you find a common denomenator for 2 fractions like 1/5 and 2/6?(52 votes)
- 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(28 votes)
- Are two fractions multiplied equals 1 called reciprocals?(9 votes)
- 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(21 votes)
- how do you find the common denominators?(7 votes)
- 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=(26 votes)
- the lowest common denominater of 1/6 and 3/6 is 12 right?(9 votes)
- No, in this case 1/6 and 3/6 already have a common denominator of 6.(28 votes)
- its too hard for me i need help.(7 votes)
- If you need help,read this excerpt.
When fractions have the same denominator, we say they have common denominators. (e.g. 1/6 has a common denominator with 2/6.)
Having common denominators makes things like comparing, adding, and subtracting fractions easier.
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.
(e.g 1/4 2/5
4,8,12,16,20
5,10,15,20
Twenty appears in both tables so, 1/10 is the same as 2/20)
Get it?(9 votes)
- 2 x 9 = 18.
2,000 has three zeros at the end, and 900 has two zeros at the end. This is a total of five zeros at the end.
So 2,000 x 900 = 1,800,000.
Have a blessed, wonderful day!(8 votes)
- how doses 1/3= 3,6,9,12,15
and 6/5=5,10,15,20,25
= 15(5 votes) - what is 7/6 i want to know what it is(5 votes)
- can get help with fractions?(4 votes)