If the numrator and the denominator (the top and the bottom numbers respectively) of a fraction have a factor in common then the fraction can be reduced by dividing both the numerator and denominator by that factor. For example, 18/24 is not in its simplest form because 2 is a common factor of 18 and 24. Dividing both 18 and 24 by 2 gives the reduced form: 9/12. But this is NOT the end of the story because 9 and 12 also have a factor in common, which is 3. Dividing both by 3 gives 3/4. This IS the end because 3 and 4 have no factor in common (they are coprime). So the original fraction is now in its reduced form. Instead of going though this process step by step, you could find the greatest common factor of the numerator and denominator and divide both by the gcf. That would be quicker if you are happy calculating gcfs.