There are many answers to this question, if you want a random answer, all you have to do is multiply both 1 and 5 by the same number. For example, 1x2=2 and 5x2=10, 2/10 is equal to 1/5. This can work for any fraction and as long as you multiply both the numerator and denominator by the same number, that fraction is equal to the other one.
and then assuming you DONT put season one back on the shelf you would then have the probablity of 1/4 because you are again choosing 1 dvd out of now 4
