Check to see if the denominator of the fractions are the same. The number above the fraction bar (the line between the numbers) is called the numerator, and the number below the fraction bar is the denominator. In order to add fractions, the denominator of the fractions must be the same.
Find the least common denominator (LCD), the smallest number that can be evenly divided by the denominator of each fraction, if the fractions have different denominators. Multiply the denominators together to find a common denominator then divide the answer by the greatest common factor (GCF), the largest number that divides evenly into the denominators.
For example, a common denominator of 1/4 and 5/24 is 96 (4 x 24). Find the GCF by listing the numbers that can be evenly divided into 4 (the factors are 1, 2, 4) and 24 (the factors are 1, 2, 3, 4, 6, 8, 12, 24). Choose the largest factor that goes into both numbers, 4. Divide the common denominator 96 by the GCF, 4, to find the LCD, 24. If finding the LCD of three or more numbers, calculate the LCD two denominators at a time.
Alternately, calculate the LCD by breaking the numbers down into their smallest factors. If your denominators are 4, 6 and 8, then you have 4 = 2 x 2; 6 = 2 x 3; 8 = 2 x 2 x 2. Multiply the factors that occur the most. In this example, the number 2 appears three times as a factor of 8 and 3 appears once as a factor of 6. Multiply 2 x 2 x 2 x 3 to find the LCD of 24.
Multiply the numerator and denominator by the same quantity to form an equivalent fraction. For example, to add 1/8 and 2/4 keep the fraction 1/8 the same (the LCD is 8) and multiply 2/4 by 2/2 -- which equals 1 and therefore does not change the value of the fraction -- to get 4/8. The problem now reads 1/8 + 4/8, and the fractions can be added because the denominators are the same.
Add the numerators together. In the example, the numerators are 1 and 4, so the sum is 5. Place this over the common denominator, 8. 1/8 + 4/8 = 5/8.