Verified Answer :

Because there is no whole number that you can divide into both the numerator and the denominator to get a proper fraction.

\(\frac{31}{33}\) is in simplest form because no whole number what so ever can be divided by d numerator and d denominator to get a proper fraction. Here are some examples in trying to divide it with whole numbers but failing:-

\(\frac{31/3}{33/3} = \frac{10.333....}{11}\)

\(\frac{31/4}{33/4}= \frac{7.75}{8.25}\)

Hope i helped ya!!