Quiz 5
NAME:
1. (10 pts) Suppose that you like to spend your Saturdays at the beach with a metal
detector looking for gold. Letâs say that 1 in 10 metal objects buried in the sand
is actually a piece of gold. Let X be the total number of times you have dug
something up after you have dug up your first piece of gold this Saturday.
Today you felt very lucky, but when you got to the beach you donât get any gold
on your first dig and get discouraged. Given that you will have to dig up at least
two things today at this point (weâll assume you wonât leave until you dig up one
piece of gold), what is the probability that you will need to dig at least 4 times
today in order to find your first piece of gold (i.e. What is P (X ? 4|X ? 2) ?
1
2. (10 pts) The taste test for PTC (phenylthiocarbamide) is a favorite exercise in
beginning human genetics classes. It has been established that a single gene determines whether or not an individual is a âtasterâ. If 70% of Americans are
âtastersâ and you are in a class of 20 students, what is the distribution, mean, and
variance of X, the number of people in the class who can taste PTC (assuming
the class represents a random sample of the american population). When naming
the distribution of X, be sure to include the parameter values for that particular
distribution.