In order to simplify a fraction, you need to divide the top and bottom
by the same number. That means that the top and bottom must have
a common factor ... you have to find that first, before you can start
simplifying. Maybe that's why they teach common factors before they
teach simplifying fractions.
Anyway, I can take one look at this fraction and see that the top and
bottom have no common factor. In fact, the top number ... 31 ... is a
prime number, so it doesn't have any factors at all, except ' 1 ' and itself.
And that's how I can tell that the fraction is in the simplest form.
