Determine how far you want the decimal carried out. This information will be detailed in the problem or by your textbook or teacher. Usually, a decimal will be carried out the the hundredths, meaning two places to the right of the decimal, or the thousandths, meaning three places to the right of the decimal. For example, if you are converting fractions for a money problem, it would be hundredths because the smallest form of currency is the penny, which is 1/100 of a dollar. If you are converting fractions for baseball players' slugging percentages, it would be to the thousandths because slugging percentages are always written in that form.
Convert the mixed fraction to a decimal. A mixed fraction means that you have some portion of the fraction that represents whole numbers and other portions that represent fractional numbers. For example, 2 1/2 means there are two whole numbers and one-half. Leave the whole numbers alone.
Next, using your calculator, perform the division for the fraction. In the example, 1/2, or one divided by two, equals 0.50 when brought out to the nearest hundredth. Therefore the conversion transforms the mixed fraction from 2 1/2 to 2.50.
Round off the last number using the rule of 5. If the last number is 5 or greater, the previous number is rounded up to the next whole number. If the number is four or less, the previous number remains the same. For example, if you were asked to convert 5 3/8 to decimal form to the nearest hundredth, perform the calculation as described in Steps 1 and 2 to get your answer.
Leave the 5 alone. Divide 3/8 using your calculator to yield a result of 5.375.
Because the last number is 5, you round the previous number up for a final answer of 5.38.
Perform this task for the other side of the equation. For example, if the problem is 3 3/16 x 7 6/9 = Y and you must solve to the nearest thousandth, solve it in this manner:
First, you would leave both the 3 and 6 alone because they are whole numbers. Divide 3 by 16 to obtain 0.1875. Then divide 6 by 9 to get 0.6667 Both of the last numbers are 5 or above, so each previous number is rounded up to read: 0.188 and 0.667.
Rewrite the equation inserting the decimals as 3.188 x 6.667 = 21.2543, or 21.254 when rounded to the nearest thousandth because 4 is less than five, so the previous number is left alone.