46. How much do you study? A survey among freshmen at a certain university revealed that the number of hours spent studying the week before

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46. How much do you study? A survey among freshmen at a certain university revealed that the number of hours spent studying the week before final exams was normally distributed with mean 25 and standard deviation 7.

c. Between what two values are the middle 80% of the hours spent studying?

20. Working two jobs: The Bureau of Labor Statistics reported in a recent year that 5% of employed adults in the United States held multiple jobs. A random sample of 75 employed adults is chosen.

b. A new sample of 350 employed adults is chosen. Find the probability that less than 6.5% of the individuals in this sample hold multiple jobs.

Section 4.2 #18 & Section 8.2 #16

18. Compute the least-squares regression line for predicting y from x given the following summary statistics:

x̄ = 8.1 sx = 1.2 ȳ = 30.4 sy = 1.9 r = −0.85

16. A sample of size n = 61 is drawn.

a. Find the critical value tα/2 needed to construct a 95% confidence interval.

b. If the sample size were n = 15, what additional assumption would need to be made for the confidence interval to be valid?

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