Review for Exam II
Econ 207
Dr. Khan
Note: Review the lecture notes, homework problems, and quizzes.
1. A set of final examination grades in an introductory statistics course was found to be
normally distributed with a mean of 73 and a variance of 64.
a. What is the probability of getting a score of 91 on this exam?
b. What percentage of students scored between 65 and 89?
c. What is the final exam grade if only 5% of the students taking the test scored lower?
2. A family has five smoke alarms in their home, all battery operated and working
independently of each other. Each has reliability of 90% - that is, has a 90% chance of
working. If fire breaks out, what is the probability that at least two of them will sound
the alarm?
3. The chance that any given taxicab in New York will be involved in an accident in any
one month is .02. If a particular cab company has 10 cabs on the street, what is the
probability that at least 4 will be in an accident this month?
4. Airplanes arrive at Chicago O’Hare airport at the average rate of 5.2 per minute. Air
traffic controllers can safely handle a maximum of four airplanes per minute. What is the
probability that airport safety is jeopardized?
5. Given the following probability distribution:
X
P(X)
0
.5
1
.2
2
--3
.10
4
.05
Find the following:
a. Expected value b. Variance c. Standard deviation.
6. Carol spent all weekend partying and knows absolutely nothing about the 10 true/false
questions on a Monday morning economics quiz. What is the probability that she gets at
least 8 right by simply guessing?
** Review all the homework problems, problems in the lecture note. Then solve this
worksheet. Good Luck!!!