Adding or Subtracting Fractions with a Like Denominator For Measuring

1. Set up the fractions for addition or subtraction. For example, if you want to double a recipe that calls for 1/3 cup, you will need to add 1/3+1/3.

2. Find the common denominator (bottom number) of the fraction. Both bottom numbers are 3 in the example, so the common denominator is 3.

3. Add or subtract the numerators (top numbers) to find the sum. When using the example, adding the numerators will be 1+1=2.

4. Place the common denominator on the bottom of the fraction, and the numerator on the top of the fraction. Therefore, you will need 2/3 cups (1/3+1/3=2/3).

Adding or Subtracting Fractions with Different Denominators for Measurements.

1. Set up the fractions for addition or subtraction. As an example, if you need 1/2 cup for four servings, and 1/4 cup for two servings, to have six servings, you will need 1/2+1/4.

2. Find the least common denominator, which in this example is 4. You arrive at this number by using prime factorization; 2=2 and 4=2x2, which leaves 4 as the least common denominator.

3. Rewrite the fraction with the new multiples, 2/4+1/4.

4. Add or subtract the numerators to find the sum, 2+1=3.

5. Place the common denominator on the bottom of the fraction, and the numerator on the top of the fraction, therefore, 2/4+1/4=3/4. So, this means that for 6 servings, you will need 3/4 cup.

Adding or Subtracting Ounce Measures

1. Use the ounce equivalent of the cup measures for altering measurements if a recipe calls for ounce measurements. 1 cup is 8 oz., 1/2 cup is 4 oz. and 1/4 cup is 2 oz.

2. Convert the cup measurements into ounces if necessary. For example, 1 cup equals 8 oz., and 1/2 cup equals 4 oz.

3. Add or subtract the ounce measurements when altering ingredient amounts. For example, 8 oz. plus 4 oz. (8+4=12) equals 12 oz.