To express the number 66 as a fraction in its simplest form, you need to write it over 1. So, you can write:
66 = 66/1
This is already in fraction form. In mathematics, a fraction is in its simplest form when the numerator and the denominator have no common factors other than 1.
Since 66 is a whole number and 1 is the lowest positive integer, there are no common factors to simplify further. Therefore, 66 expressed as a fraction in simplest form is:
66/1