Fractions in Simplest Form

A fraction is said to be in simplest form if its numerator and denominator are relatively prime, that is, they have no common factors other than 1 . (Some books use "written in lowest terms" to mean the same thing.)

So, 5 9 is in simplest form, since 5 and 9 have no common factors other than 1 . But 6 9 is not; 6 and 9 have a common factor 3 .

To write 6 9 in simplest form, divide both the numerator and denominator by the greatest common factor, in this case 3 :

6÷3 9÷3 = 2 3

So 6 9 in simplest form is 2 3 .

This is known as reducing fractions.