Researchers for a company that manufactures batteries want to test the hypothesis that the mean battery life of their new battery is greater than the known mean battery life of their older version. The researchers selected random samples of 32 of the new batteries, subjected the batteries to continuous use, and determined the mean and standard deviation of the battery lives in the sample. Which of the following is an appropriate test for the researchers' hypothesis? a. A one-sample z-test for a population mean.
b. A one-sample t-test for a population mean.
c. A one-sample z-test for a population proportion.
d. A matched-pairs t-test for a mean difference
e. A two-sample t-test for a difference between means