7.79 Students at a university in Ghent, Belgium, are expected to complete a group presentation in 20 minutes as one of the assessments to pass the business module. In a random sample of 18 presentations, the module leader finds a mean duration of 17 minutes with a standard deviation of 5 minutes. Find the 98% confidence interval for estimating the duration of each group presentation and recommend the maximum duration for the group presentation.

7.80 Everyone knows that drinking enough water is important.

A health campaign is conducted at a residential area to determine whether the residents drink enough water per day. From a random sample of 26 residents, the mean amount of water consumed per day is 2.8 liters with a standard deviation of 0.5 liters. Find a 95% interval estimate of the mean daily amount of water consumed by all residents.