Problem 1: In the book A Guide to the Development and Use of the Myers–Briggs Ty
ID: 3218069 • Letter: P
Question
Problem 1: In the book A Guide to the Development and Use of the Myers–Briggs Type Indicators by Myers and McCaully, it was reported that approximately 45% of all university professors are extroverted. Suppose you have classes with six different professors.
(a) What is the probability that all six are extroverts?
(b) What is the probability that none of your professors is an extrovert?
(c) What is the probability that at least two of your professors are extroverts?
(d) In a group of six professors selected at random, what is the expected number of extroverts? What is the standard deviation of the distribution?
(e) Suppose you were assigned to write an article for the student newspaper and you were given a quota (by the editor) of interviewing at least three extroverted professors. How many professors selected at random would you need to interview to be at least 90% sure of filling the quota?
Explanation / Answer
p = 0.45
a) p(6 are extroverts) = (0.45)^6 = 0.0083
b) p( none of professor is extrovert) = 1 - p = 1 -0.45 = (0.55) ^6 =.0277
c) p(at least two ) = 1 - 6C0 * 0.45^0 * 0.55^6 - 6C1 * 0.45^1 * 0.55^5
= 0.8364
d)
E[X] = np = 6(0.45) = 2.7
s = sqrt(np ( 1 -p )) = sqrt ( 2.7 * 0.55) = 1.219