In order to add mixed number in fractions, in a math problem, you will need to focus on the denominator. The denominator is the lower number in the fraction. The top number is called the numerator. When you look at the denominator, you should try to figure out if the denominators of the fractions have any number in common. If they don't have a common factor, then you will need to multiply them by each other: for example, 2/3 and 3/4 do not have a common factor. Therefore, you will need to multiply 2/3 by four, and you will have to multiply 3/4 by 3. This will give you 8/12 and 9/12. When you add them together, you will get 17/12. When you simplify it, you are done. Divide 17 by 12, and you get 1 5/12.