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Chapter Problems
Problem 1
The mean amount of gasoline and services charged by Key Refining Company credit customers is $70 per
month. The distribution of amounts spent is approximately normal with a standard deviation of $10.
Compute the probability of selecting a credit card customer at random and finding the customer charged
between $70 and $83 last month.
Problem 2
Again using the Key Refinery data from Problem 1, compute the probability of customers charging
between $57 and $83 per month.
Problem 3
Using the Key Refining data from Problem 1, what is the probability that a particular customer charges
less than $54?
Problem 4
Again using the Key Refining data from Problem 1, compute the probability of a customer charging
between $82 and $92.
Problem 5
Key Refining (Problem 1) decided to send a special financing plan to charge account customers having
the highest 10 percent of the money charges. What is the dividing point between the customers who
receive the special plan and those who do not?
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Chapter 6
The Normal Probability Distribution
Exercise 6.1
Check your answers against those in the ANSWER section.
A cola-dispensing machine is set to dispense a mean of 2.02 liters into a bottle labeled 2 liters. Actual
quantities dispensed vary and the amounts are normally distributed with a standard deviation of 0.015
liters.
a.
What is the probability a bottle will contain between 2.02 and 2.04 liters?
b.
What is the probability a bottle will contain between 2.00 and 2.03 liters?
c.
What is the probability a bottle will contain less than 2 liters?
d.
How much cola is dispensed in the largest 4% of the drinks?
Problem 6
The Key Refining Company, referred to in the earlier problems, determined that 15 percent of its
customers do not pay their bill by the due date. What is the probability that for a sample of 80 customers,
less than 10 will not pay their bill by the due date?
Exercise 6.2
Check your answers against those in the ANSWER section.
A new drug has been developed that is found to relieve nasal congestion in 90 percent of those with the
condition. The new drug is administered to 300 patients with this condition. What is the probability that
more than 265 patients will be relieved of the nasal congestion?
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Chapter 6
The Normal Probability Distribution