Download Notes on SD of sample proportions

The average age of a vehicle registered in the United
States is 96 months. Assume the standard deviation
is 16 months. If a random sample of 36 cars is
selected, find the probability that the mean of their
age is between 90 and 100 months.
Sampling Distribution
of Sample Proportions
General Properties
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p  p
npq
npq
npq



 p 
2
2
n
n
n

Approximately normal if
pq
n
Proportion of all cardiac patients receiving blood
transfusions who contract hepatitis was 0.07. A new
screening is believed to reduce this incidence rate. It’s
given to 200 blood recipients. What’s the probability that
less than 6 of the 200 contract hepatitis.
Assume that 30% of students at a university wear
contact lenses. We randomly select 100 students.
What is the probability that more than one-third of
this sample wear contacts?
The library says that 60% of people like to read
murder mysteries. What’s the probability that at
least 32 out of 60 people will prefer to read a murder
mystery?
A school claims that 98% of its students pass the exit
exam. What's the probability that less than 96% of
the 100 students that takes the exam passes the
test.
The average price of a pound of bacon is $2.02.
Assume the standard deviation is $0.08. If a random
sample of 40 one-pound packages is selected, find
the probability that the mean of the sample will be
less than $2.00.
Approximately 62% of all freshmen loose their Life
scholarship by the end of their sophomore year.
What’s the probability that in a group of 40, more than
26 have lost their life scholarship.
Homework
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Worksheet