MATH 218 SI Session (Spring 2008)
SI Leader: Mario
Week 14
Worksheet Tuesday (4/15/08)
Professor: Zygouras/Dumett
www.usc.edu/si
1.
The number of students entering the bookstore is Poisson distributed with an average rate
of 2 students every 3 minutes.
a.
What is the probability that at most 1 student enters the bookstore in the next 2
minutes?
b.
Find the probability that the next student arrives within half a minute.
c.
What is the probability that no students enter within the next two minutes?
d.
What is the average time between students?
2.
With the high demand for many of the new video consoles, there is only a 25% chance
that any store will carry the exact system that you are looking for this holiday season.
a.
Suppose we decided to visit 20 different stores.
What is the probability that we
find the system that we want at exactly 5 out of the 20 stores?
b.
Find the expected value and standard deviation for the number of stores that carry
the system that you are looking for.
c.
What is the probability that more than 18 out of the 20 stores carry the system that
we are looking for?
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3.
The Elgin Heart Institute performs many openheart surgery procedures. Recently
research physicians at Elgin have developed a new heart bypass surgery procedure that
they believe will reduce the average recovery time. The hospital will not recommend the
new procedure unless there is substantial evidence to suggest that it is better than the
existing procedure. Records indicate that the current mean recovery time for the standard
procedure is 42 days, with a standard deviation of 5 days. To test whether the new
procedure actually results in a lower mean recovery time, it was performed on a random
sample of 36 patients. Assume the standard deviation remains 5 days.
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 Spring '06
 Haskell
 Math, Standard Deviation, Statistical hypothesis testing

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