To convert a mixed number to an improper fraction, multiply the denominator by the whole number out front, then add the numerator. Keep the denominator. For example:
12 1/2 = 2 * 12 + 1 = 25/2
9 1/4 = 4 * 9 + 1 = 37/4
Multiply 25/2 by 2/2 to have a common denominator:
25/2 * 2/2 = 50/4
50/4 - 37/4 = 13/4 or 4 1/3
