COMMON DENOMINATORS

1. When fractions have the same number in the denominator, they are said to have COMMON DENOMINATORS. For example: 1/9, 2/9, 5/9, 7/9, and 3/9 all have a COMMON DENOMINATOR of 9.

2. Remember! Before fractions may be added or subtracted, the denominators of all the fractions in the problem must be the same.

  1. Rules:
Denominator = B

Numerator = A

 1. If A and the B of a fraction are multiplied by the same number, the value will not change. Example: 1/4 x 2 = 2/8 1/8 x 2 = 2/16 The result is 2/8 and 3/12 are same value. 2. If the A and the B of a fraction are divided by the same number, the value of the fraction will not change. Example: 3/9 : 3 => 3 : 3 and 9 : 3 => 1/3

1/3 still have the same value with 3/9

 

 To find COMMON DENOMINATOR for the fractions 1/4, 3/8, and 5/16: (1) Find the largest denominator.

(The largest denominator is 16.)

(2) See if the other denominators can be divided into 16 an even number of times. (4 and 8 can both be divided into 16 an even number of times.)
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