what is the common denominator for 3/4 and 2/5

Question

What is the common denominator for 3/4 and 2/5

Answer 1

Hi Elikem!

 

 

To find the common denominator. First check to see if one of the numbers is divisible by the other.  In this case 4 is not divisible by 5 and 5 is not divisible by 4.  So the next step is to find the common multiple.

You do this by writing out the multiples of each.

 

4  8  12  16  20  24  28

5  10  15  20  25

 

When you find a common multiple, in this case 20, you have found the common denominator. 

Hope this helps!
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Answer 2

Hi Elikem.

 

The common denominator is what both fractions are equal to where their denominator is the same.

 

So for our problem - we need to change both fractions to an equal form where their denominator matches.

 

How do you change a fraction's denominator without changing its value?  Multiply it by 1.

So 3/4 times 2/2 (which equals 1) = 6/8.  This is the same value - just in a different form.

 

So what if we multiply each of the fractions in your problem by the other fraction's denominator?

3/4 times 5/5 = 15/20.

2/5 times 4/4 = 8/20.

 

Do you agree that each of these changes in form are equal to their original fraction?

So your lowest common denominator is 20.

Answer 3

I always start these by cross-multiplying the two fractions:

 

3*5/4*5 =15/20

4*2/4*5 = 8/20

 

The question now is can we divide the 15 or the 8 by a common factor and get whole numbers..

 

Try 2.... get 7.5 and 4

Try 3.... get 5 and 8/3

Try 5... get 3 and 8/5

 

Therefore the lowest common denominator is 20.

 

 

 

Answer 4

Hi Elikem,

 

For the given fraction,

 

3/4 and 2/5 the common denominator is the product of the individual denominators

 

denominator =4*5=20