Page 74 - Applied Statistics And Probability For Engineers

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2-8 RANDOM VARIABLES 57

2-119. The following table lists the history of 940 orders for each device is as shown. What is the probability that the
features in an entry-level computer product. circuit does not operate?
extra memory
0.02
no yes
optional high- no 514 68
speed processor yes 112 246
0.01 0.01
Let A be the event that an order requests the optional high-
speed processor, and let B be the event that an order requests
extra memory. Determine the following probabilities: 0.01 0.01
(a) P1A ´ B2 (b) P1A ¨ B2
(c) P1A¿´ B2 (d) P1A¿¨ B¿2
(e) What is the probability that an order requests an optional 0.02
high-speed processor given that the order requests extra
memory?
2-122. A company that tracks the use of its web site deter-
(f) What is the probability that an order requests extra mem-
mined that the more pages a visitor views, the more likely the
ory given that the order requests an optional high-speed
visitor is to provide contact information. Use the following ta-
processor?
bles to answer the questions:
2-120. The alignment between the magnetic tape and head
in a magnetic tape storage system affects the performance of Number of
the system. Suppose that 10% of the read operations are de- pages viewed: 1 2 3 4 or more
graded by skewed alignments, 5% of the read operations are
Percentage of
degraded by off-center alignments, and the remaining read op-
visitors: 40 30 20 10
erations are properly aligned. The probability of a read error is
Percentage of visitors
0.01 from a skewed alignment, 0.02 from an off-center align-
in each page-view
ment, and 0.001 from a proper alignment.
catgory that provide
(a) What is the probability of a read error?
contact information: 10 10 20 40
(b) If a read error occurs, what is the probability that it is due
to a skewed alignment? (a) What is the probability that a visitor to the web site
2-121. The following circuit operates if and only if there is provides contact information?
a path of functional devices from left to right. Assume that de- (b) If a visitor provides contact information, what is the
vices fail independently and that the probability of failure of probability that the visitor viewed four or more pages?