Just divide that numerator by the denominator, long-division-style.
Example 2
Convert to a decimal.
Division time, baby. Divide the numerator (2) by the denominator (9).
If we fall into a pattern in our long division of getting the same remainder again and again and again, we write the repeating number in the quotient with a bar over it, meaning that it keeps going forever.
Example 3
Use long division to prove that the following equation is true.
If the fraction we need to convert is a mixed number, we can find the decimal version of the fraction by itself first, then add the whole number at the end.
Start by dividing the numerator (17) by the denominator (20).
So the fraction part comes out to 0.85. Add the whole number 2 from the beginning and we've got 2.85. Yep, the equation is true.