Two Means - Known Variance: Videos & Practice Problems

A technology company claims that the average battery life of its new phone model is longer than that of a competitor's model. A sample of $36$ phones from the new model has a mean battery life of $18$ hours (population standard deviation is $2.5$ hours). A sample of $30$ phones from the competitor's model has a mean of $16.5$ hours (population standard deviation is $2.8$ hours). Decide whether the hypothesis test is left-tailed, right-tailed, or two-tailed, and whether to use a $z$-test or a $t$-test.