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9.2 Name Curtis Smith 1) Suppose a 90% confidence interval for u turns out to be (1000, 2100). If this interval was based on a sample of size n = 25, explain what assumptions are necessary for this interval to be valid. A) The sample was randomly selected from a skewed population. B) The sample was randomly selected from an approximately normal population. C) The population of salaries must have an approximate t distribution. D) The sampling distribution must be biased with 24 degrees of freedom. 2) To select the correct Student's t-distribution requires knowing the degrees of freedom. How many degrees of freedom are there for a sample of size n? A) n + 1 B) n On-1 D) (x - H)/ (s/ n) 3) Determine the point estimate of the population mean and margin of error for the confidence interval with lower bound 29 and upper bound: 45. A x = 37, E = 8 B) X = 37, E = 16 C) X = 29, E = 16 D) X = 45, E = 8 4) The grade point averages for 10 randomly selected high school students in Ohio are used to find a confidence interval. What is the effect on the width of the confidence interval if the sample size is increased to 20? The width decreases. B) The width remains the same. ") The width increases. 5) Construct a 95% confidence interval for the population mean, u. Assume the population has a normal distribution. A sample of 20 part-time workers had mean annual earnings of $3120 with a standard deviation of $677. Round to the nearest dollar. A) ($2803, $3437) B) ($1324, $1567) C) ($2135, $2567) D) ($2657, $2891) Interpret this interval: 96% of intervals constructed in this manner should Contain the population mean of uil is between $2803 and we are $361370