STAT 210
FOCUS EXERCISE 12
1.
Of interest is to estimate the proportion of all students who contact SCHEV that attend the
Virginia
Community College
system (code
C
). The goal is to do this by calculating a 95% confidence interval with
margin of error no larger than .07. What is the minimum sample size required that guarantees that this can be
done? Note that the data presented in question 2 cannot
be used to solve this question.
0.07 = 1.960 x sqrt (0.5(10.5)/n)
n = 196
2.
SCHEV obtained a simple random sample of 200 students who have contacted them and determined which
of the five types of institutions they attend. Using the codes listed above, the results were as follows.
4 = 96/200 = 0.48
2 = 12/200 = 0.06
C = 44/200 = 0.22
P = 42/200 = 0.21
V = 6/200 = 0.03
For each of the five institution types listed above, determine the proportion of the sample of 200 students who
fall in each category. Note that these proportions, when added together, should sum to 1.
3.
If appropriate, use the information in question 2 to calculate and interpret
a 90% confidence interval for the
proportion of all students who contact SCHEV that attend
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 Fall '06
 Basu
 private colleges, SCHEV

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