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Math 311. Probability and Statistics I
Midterm #1
Your name:
Reminder: Explain your answers. Show your work.
1
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(1) (20pts) Seventy percent of the light aircraft that disappear while in ﬂight
in a certain country are subsequently discovered. Of the aircraft that are
discovered, 60% have an emergency locator, whereas 90% of the aircraft not
discovered do not have such a locator. Suppose a light aircraft has disap
peared.
a) If it has an emergency locator, what is the probability that it will not
be discovered ?
b) If it does not have an emergency locator, what is the probability that it
will be discovered ?
3
(2) (20 pts) Consider this experiment: I throw two (fair and independent) dice,
and observe the sum of the two numbers. I keep throwing until I see a sum
of either 7 or 8, then I stop. So an example of an outcome is (3
,
5
,
8), another
example is (9
,
5
,
3
,
2
,
9
,
7), yet another example is (8).
(Warning: do not mix up this problem with the one in the sample exam.)
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This note was uploaded on 11/14/2010 for the course MATH 311 taught by Professor Yu during the Spring '08 term at Drexel.
 Spring '08
 YU
 Statistics, Probability

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