SOLUTION: 13/15 - 11/20 = Help again please, just need to no how to do these again. My mind is not of any help need proffesionals...

Question 108069: 13/15 - 11/20 =
Help again please, just need to no how to do these again. My mind is not of any help need proffesionals...
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
requires that you find a common denominator. It is usually most convenient to find the lowest common denominator.
:
First begin with the prime factorization of 15, which is 3 * 5.
:
Then find the prime factorization of 20, which is 2 * 2 * 5.
:
Therefore, the lowest common denominator has two factors of 2, one factor of 3, and one factor of 5, i.e. 2 * 2 * 3 * 5 = 60.
:
Now you can multiply each of your fractions by 1 in the form of some where a = 60 divided by the denominator of the fraction.
:
so multiply the first fraction times :
:

:
Similarly, , so
:
Now your problem reads:
:

:
Since the denominators are now equal, you can add the numerators directly to get the requested sum:
:

:
Just to show the convenience of finding the lowest common denominator, if you had just multiplied the two denominators together to get a convenient common denominator that wasn't necessarily the lowest, in this case 300, you would have had the following result:
, and is a rather messy fraction to have to reduce to lowest terms. I'll leave it as an exercise for you to prove that .

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