Multiply the leading integer of the mixed number with the denominator, add the numerator to that product and then replace the original numerator with the new sum. These mathematical operations change the expression into an improper fraction. For this example, the first mixed number is 5 1/2. Multiplying 5 by 2 results in 10, and adding the numerator 1 to 10 equals 11. Placing 11 as the new numerator results in 11/2.
Change the next expression into an improper fraction. For this example, the other mixed number is 4 1/3. Following the previous step, multiplying 4 by 3 results in 12, and 1 added to 12 is 13. Placing 13 as the new numerator results in 13/3.
Multiply the first numerator by the other numerator, then multiply the first denominator by the second one, and then set the numerators' product as the new numerator and the denominators' product as the new denominator. For this example, 11 multiplied by 13 equals 143, and 2 and 3 multiplied together equals 6. Placing 143 as the numerator and 6 as the denominator results in 143/6.