Begin with two mixed numbers to subtract. For example, 8 2/3 - 2 1/4.
Subtract the smaller integer from the larger one. So, 8 - 2 = 6.
Find a common denominator of 2/3 and 1/4. Look at the multiples of each number and find the lowest one that they share. For example, the multiples of 3 are 3, 6, 12, 15, 18 and 20, while the multiples of 4 are 4, 8, 12, 16 and 20. Therefore, 12 is lowest common denominator.
Change the fractions so they reflect the new common denominator. For 2/3, 3 goes into 12 four times, so multiply 2 x 4 = 8/12. Then 4 goes into 12 three times, so multiply 3 x 1 = 3/12.
Subtract the fractions: 8/12 - 3/12 = 5/12.
Put the new integer in front of the fraction: 6 5/12. Therefore, 8 2/3 - 2 1/4 = 6 5/12.