Common fractions describe rational numbers as ratios of one integer divided by another integer. The top or first part of a common fraction is the numerator, and the bottom or second part of the fraction is the denominator. The denominator cannot be zero because a number divided by zero is undefined or infinity. The reciprocal of a fraction is the number created by switching the numerator and the denominator. If the number is a whole integer, then the reciprocal is one over the integer. Reduce a common fraction when possible by dividing down the numerator and the denominator with any common integer divisors. A fraction in proper form also has a numerator smaller than the denominator. If the absolute value of the numerator is greater than the absolute value of the denominator, then convert the fraction to an integer combined with a common fraction in proper form. Conversion to the proper form is done by dividing the numerator by the denominator. Since a common fraction is a rational number it can also be expressed as a decimal fraction. A common fraction cannot represent an irrational number, because irrational numbers cannot be expressed as one number divided another number.

Converting a common fraction to proper form:
6/8 = ¾, 6 and 8 can both be divided by two
12/3 = 4, 3 goes into 12 four times
0/5 = 0, zero divided by anything is zero
3/2 = 1½, 3 is greater than 2 and 2 goes into 3 one and a half times
11/4 = 2¾, 4 goes into 11 two and three quarter times, and if the integer 2 is multiplied by the denominator 4, then added to the numerator 3 it equals 11.