How to Add and Subtract Fractions with Unlike Denominators

When you're adding fractions with an unlike denominator you make a common denominator by multiplying it with each other or if one denominator is the answer to the other denominator you multiply the factor and don't change the other fraction it stays like that until you add. So when you multiply the denominator you multiply the numerator with that multiple. Then you add it but you don't add your denominator because that tells you how many equal pieces make a whole. You only add the numerator. After you put it into lowest terms, if there are any. When you're subtracting its the exact same but you just have to subtract instead of add.

Examples: 

2  x4 +  1 x3
3 x4      4 x3

 8    +    3      =   11
12         12          12


7       +      7 x3   
12             4 x3

7       +       21      =   28
12              12            12