1. The vitamin C content of a random sample of 40 school lunches in the Bellevue school district produced a sample
mean equal to 7.6mg and the standard deviation was 3.1mg. Describe in words what µ represents in this problem.
Then, find a 90 percent confidence interval for µ. Answer: 7.6
0.806
2. In problem 1, set a 95% confidence interval for µ. Answer: 7.6
0.980 (using z=2; 7.6 0.961 with 1.96)
3. Due to variation in laboratory techniques, impurities in materials, and other unknown factors, the results of an
experiment in a chemistry lab will not always yield the same numerical answer. In an electrolysis experiment, a class
measured the amount of copper precipitated from a saturated solution of copper sulfate over a 30-minute period. The
n=45 students acquired a sample mean and standard deviation equal to .145 and .0051 moles, respectively. Set a
90% confidence interval on µ, the true unknown mean amount of copper that could be precipitated from the solution
in 30-minutes. Answer: 0.145
.00125
4. In problem 3, set a 95% confidence interval on µ. Answer: 0.145
.00152 with 2 as tabled value; with 1.96, you
get 0.145 .00149.
5. Measurements of water intake, obtained from a sample of 37 rats that had been injected with a sodium chloride
solution, produced a mean and standard deviation of 31.0 and 6.3 cubic centimeters, respectively. Set a 98%
confidence interval on the population mean µ, after first describing verbally what µ represents in this problem.
Answer 31.0 2.42.
Math 311 Fall 2008 Worksheet 17 Large Sample Confidence Intervals for a
population mean
