# Chapter 4-3:

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Let event A= subject is telling the truth and event B= polygraph test indicates that the subject is lying. Use your own words to translate the notation P(B|A) into a verbal statement.

a) The probability that the polygraph indicates lying given that the subject is actually telling the truth.
b) The probability that the polygraph indicates laying given that the subject is actually lying.
c) The probability that the polygraph indicates truthfulness given that the subject is actually telling the truth.
d) The probability that the polygraph indicates truthfulness given that the subject is actually lying.
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Let event A= subject is telling the truth and event B= polygraph test indicates that the subject is lying. Use your own words to translate the notation P(B|A) into a verbal statement.

a) The probability that the polygraph indicates lying given that the subject is actually telling the truth.
b) The probability that the polygraph indicates laying given that the subject is actually lying.
c) The probability that the polygraph indicates truthfulness given that the subject is actually telling the truth.
d) The probability that the polygraph indicates truthfulness given that the subject is actually lying.
In an experiment, college students were given either four quarters or a $1 bill and they could either keep the money or spend it on gum. The results are summarized in the table. Complete parts 1 through 3 below. Students Given Four Quarters Purchased Gum - 34 Kept the Money - 12 Students Given a$1 Bill
Purchased Gum - 17
Kept the Money - 33

1. Find the probability of randomly selecting a student who spent the money, given that the student was given four quarters.

2. Find the probability of randomly selecting a student who kept the money, given that the student was given four quarters.

3. What do the preceding results suggest?
a) A student given four quarters is more likely to have kept the money.
b) A student given four quarters is more likely to have kept the money than a student given a $1 bill. c) A student given four quarters is more likely to have spent the money than a student given a$1 bill.
d) A student given four quarters is more likely to have spent the money.
1. Find the probability of randomly selecting a student who spent the money, given that the student was given four quarters. 0.739
Add together all the student who were given Four Quarters. 46
34/46=0.739

2. Find the probability of randomly selecting a student who kept the money, given that the student was given four quarters.0.261
Add together all the students who were given Four Quarters. 46
12/46=0.261

3. What do the preceding results suggest?
d) A student given four quarters is more likely to have spent the money.
The data represent the results for a test for a certain disease. Assume one individual from the group is randomly selected. Find the probability of getting someone who tests negative, given that he or she did not have the disease.

The Individual Actually Had the Disease
Positive
Yes - 126
No - 38
Negative
Yes - 5
No - 131

The probability is approximately _____.
The accompanying table shows the results from a test for a certain disease. Find the probability of selecting a subject with a negative test result, given that the subject has the disease. What would be an unfavorable consequence of this error?

The Individual Actually had the Disease
Positive
Yes - 334
No - 2
Negative
Yes - 19
No - 1179

The probability is ______.

What would be an unfavorable consequence of this error?
a) The subject would not receive treatment and could spread the disease.
b) The test would be shown to be not reliable.
c) The subject would experience needless stress and additional testing.
d) The test would be shown to be not effective.
The table below displays results from experiments with polygraph instruments. Find the positive predictive value for the test. That is, find the probability that the subject lied, given that the test yields a positive result.

Did the Subject Actually Lie?
Positive Test Results
No (did not lie) - 19
Yes (lied) - 42
Negative Test Results
No (did not lie) - 30
Yes (lied) - 10

The probability is _____.
Assume that there is a 7% rate of disk drive failure in a year.

1. If all your computer data is stored on a hard disk drive with a copy stored ona second disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive?

With two hard disk drives, the probability that catastrophe can be avoided is _____.

2. If copies of all your computer data are stored on three independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?

With three hard disk drives, the probability that catastrophe can be avoided is __________.