Stat 4706 HW 2 Solutions
Total Points Possible: 26
Instructions: Show all work. Calculations of x-bar and s and intermediate calculations may be done with a
calculator or software, but do not use any software programs to generate the interval for you.
1) Methyl t-butyl ether (MTBE) is an organic water contaminant that often results from gasoline spills. The level of
MTBE is thought to follow a normal distribution. The level of MTBE (in parts per billion) was measured for a
sample of 12 well sites located near a gasoline service station in New Jersey, with the following results: 150, 367,
38, 11, 134, 12, 251, 63, 8, 13, 107.
a) Find a point estimate for the population mean MTBE level for all well sites located near that NJ gasoline station.
b) Calculate a 90% confidence interval for the population mean.
c) Calculate a 99% confidence interval for the population mean. What happens to the width of the interval when we
increase the confidence level?
Worth 2 points
Worth 2 points: -1 if formula
correct bur answer is wrong
Worth 1 point: -1 if relationship
between confidence level and
interval width is not mentioned
