The definition of percent is out of one hundred. per = out of, cent = hundred
You can turn any fraction into a decimal by dividing the numerator by the denominator (the top by the bottom), and you can turn any decimal into a percentage by moving the decimal point to the right two places.
Example: 3/4 turns into 0.750, and 0.750 turns into 75.0%
In doing this, it's easier to find whether or not two fractions or decimals are equivalent, because they're in the same form, and you don't have to go through the hassle of finding a common denominator.