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# Ejercicios 56-88 56. Assume the likelihood that any flight on Northwest Airlines arrives within 15 minutes of the scheduled time is .90. We select

56. Assume the likelihood that any flight on Northwest Airlines arrives within 15 minutes of
the scheduled time is .90. We select four flights from yesterday for study.
a. What is the likelihood all four of the selected flights arrived within 15 minutes of the
scheduled time?
b. What is the likelihood that none of the selected flights arrived within 15 minutes of
the scheduled time?
c. What is the likelihood at least one of the selected flights did not arrive within 15 minutes
of the scheduled time?

57. There are 100 employees at Kiddie Carts International. Fifty-seven of the employees are
production workers, 40 are supervisors, 2 are secretaries, and the remaining employee
is the president. Suppose an employee is selected:
a. What is the probability the selected employee is a production worker?
b. What is the probability the selected employee is either a production worker or a supervisor?
c. Refer to part (b). Are these events mutually exclusive?
d. What is the probability the selected employee is neither a production worker nor a
supervisor?

59. The probability that a cruise missile hits its target on any particular mission is .80. Four
cruise missiles are sent after the same target. What is the probability:
a. They all hit the target?
b. None hit the target?

66. A recent survey reported in BusinessWeek dealt with the salaries of CEOs at large corporations
and whether company shareholders made money or lost money.
CEO Paid More CEO Paid Less
Than \$1 Million Than \$1 Million Total
Shareholders made money 2 11 13
Shareholders lost money 4 3 7
Total 6 14 20
If a company is randomly selected from the list of 20 studied, what is the probability:
a. the CEO made more than \$1 million?
b. the CEO made more than \$1 million or the shareholders lost money?
c. the CEO made more than \$1 million given the shareholders lost money?
d. of selecting 2 CEOs and finding they both made more than \$1 million?

72. Two boxes of men’s Old Navy shirts were received from the factory. Box 1 contained 25
mesh polo shirts and 15 Super-T shirts. Box 2 contained 30 mesh polo shirts and 10
Super-T shirts. One of the boxes was selected at random, and a shirt was chosen at random
from that box to be inspected. The shirt was a mesh polo shirt. Given this information,
what is the probability that the mesh polo shirt came from box 1?

73. With each purchase of a large pizza at Tony’s Pizza, the customer receives a coupon that
can be scratched to see if a prize will be awarded. The odds of winning a free soft drink
are 1 in 10, and the odds of winning a free large pizza are 1 in 50. You plan to eat lunch
tomorrow at Tony’s. What is the probability:
a. That you will win either a large pizza or a soft drink?
b. That you will not win a prize?
c. That you will not win a prize on three consecutive visits to Tony’s?
d. That you will win at least one prize on one of your next three visits to Tony’s?

77. A new chewing gum has been developed that is helpful to those who want to stop smoking.
If 60 percent of those people chewing the gum are successful in stopping smoking, what
is the probability that in a group of four smokers using the gum at least one quits smoking?

88. ABC Auto Insurance classifies drivers as good, medium, or poor risks. Drivers who apply
to them for insurance fall into these three groups in the proportions 30 percent, 50 percent,
and 20 percent, respectively. The probability a “good” driver will have an accident
is .01, the probability a “medium” risk driver will have an accident is .03, and the probability
a “poor” driver will have an accident is .10. The company sells Mr. Brophy an insurance
policy and he has an accident. What is the probability Mr. Brophy is:
a. A “good” driver?
b. A “medium” risk driver?
c. A “poor” driver?

a. A “good” driver? b. A “medium” risk driver? c. A “poor” driver?

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