Determine two fractions that you want to subtract. For example, subtract 1/2 from 3/4.
Find the number into which both denominators divide evenly to determine the lowest common denominator. You must make both denominators the same number in order to subtract the fractions. For example, 4 is the lowest common denominator of 2 and 4.
Divide the lowest common denominator by the smaller denominator. Then multiply the numerator and the denominator of the fraction with the smaller denominator by the result to convert it into an equivalent fraction with the same denominator as the larger fraction. For example, divide 4 by 2, which equals 2. Then multiply 1 by 2, which equals 2 for the numerator, and multiply 2 by 2, which equals 4 for the denominator. This converts 1/2 into the equivalent fraction 2/4.
Draw two circles on a sheet of paper and divide each of them into equal parts, the number of which is equal to the fractions' denominators. For example, the fractions' denominators are both 4, so draw two circles and divide each of them into 4 equal parts. This results in two pies each cut into 4 equal pieces.
Identify the larger fraction's numerator and color in that many pieces of the first pie. For example, the larger fraction's numerator is 3, so color in 3 pieces of the first pie. This results in 3 out of the 4 pieces of the first pie colored in, which represents the fraction 3/4.
Identify the smaller fraction's numerator and color in that many pieces of the second pie. For example, the smaller fraction's numerator is 2, so color in 2 pieces of the second pie. This results in 2 out of the 4 pieces of the second pie colored in, which represents the fraction 2/4.
Subtract the number of pieces of the second pie from the first pie to subtract the fractions' numerators. The denominators remain the same. For example, the second pie has 2 pieces, so subtract 2 pieces from the 3 pieces in the first pie. This leaves 1 piece of pie left out of 4 pieces. This represents subtracting 2/4 from 3/4, which leaves the fraction 1/4.