Professor Mean Is Planning the Big Statistics Department Super Bowl

Professor Mean is planning the big Statistics Department Super Bowl party.
Statisticians take pride in their variability, and it is not certain what kinds of chips
people will choose. Professor Mean takes a 4-sided die to the grocery store, starts at
one end of the chips aisle, and travels to the other end. For each different kind of
chip, Dr. Mean rolls the die. If it comes up a 4, she purchases a bag of those chips for
the party. There are 40 different kinds of chips in the aisle. Define random variable
x  number of types of chips purchased out of the 40 types available.
a) Random variable x is a binomial random variable. What is the mean of the
random variable x?
b) What is the standard deviation of the random variable x?