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Math 140: Statistics, April 17, 2008
Quiz 15, Chapter 21: Accuracy of Percentages
1. (4 pts.) Probabilities are used when reasoning from the _____ to the _____;
confidence levels are used when reasoning from the _____ to the _____.
Options: box, draws
2. In a hypothetical university with an enrollment of 50,000 students, a simple random
sample of 100 students found that 20 had repeated a course.
a) (4 pts.) Estimate the percentage of students in the university that have repeated a
course as a give-or-take number.
b) (4 pts.) Give a 68%- and a 95%-confidence interval for the percentage of students
repeating a course.
c) (4 pts.) If 80 students out of a sample of 400 students had repeated a course, how
would the 95% confidence interval change? Give a numerical answer.