Ch 8 FRQ Practice: Answer Questions on separate paper and submit on GC. Do not type the answers. Period 6
1. A battery manufacturer has designed a new battery to have a normal distribution
with a mean running time of 120 hours of use, A simple random sample of 18
batteries was taken with a mean running time of 132.6 hours and a standard
deviation of 5.3 hours.
(a) Construct and interpret a 98% confidence interval for the true mean running time of the
new battery.
(b) Does the interval in part (a) give convincing evidence that you think the new battery is
going to over 120 hours? Explain your reasoning.
2. The Mars chocolate company puts 24% of yellow M & M in each packet. A simple
random sample of 250 M & M’s finds that 68 are yellow.
(a) Construct and interpret a 95% confidence interval for the proportion of yellow M & M’s in each packet.
(b) Does the interval in part (a) give convincing evidence that each packet has the right proportion of yellow M & M’s? Explain your reasoning.
(c) How large a random sample is required to obtain a margin of error of at most 0.05 with 95% confidence?
(d) In part (a) you constructed a 95% confidence interval for the proportion of yellow M & M’s in each packet. Explain what you would do to the sample size to make the length of the interval to be half as wide?