From a random sample of 25 days in a recent year, gasoline prices had a mean of 51.25 pesos and a standard 5.32 pesos. Construct a 99% confidence interval for the population mean.

A Gallup poll of 1487 adults showed that 43% of the respondents have Facebook pages.  Construct a 95% confidence interval for the proportion of adults who have a Facebook page.

In a recent year, a sample of the South American Redeye Piranha was collected by fishermen on a particular river. Wildlife biologists regard this sample as a random sample of all Redeye Piranha in that river. The mean length of the 60 fish in the sample was 12.88 cm, and a 99% confidence level for the true mean length of all Redeye Piranha in that river is 12.09 cm to 13.67 cm.  Explain what would happen to the length of the interval if the confidence level were decreased to 95%.

According to a study of 90 truckers, a trucker drives, on average, 560 miles per day.  If the standard deviation of the miles driven per day for the population of truckers is 40, find the 95% confidence interval of the mean number of miles driven per day by all truckers.