The average lifetime of an oak tree is found to be 55 years from a sample of 10 oak trees. Previous records indicate that the standard deviation is 15 years when the results follow a Gaussian distribution. Construct a 99% confidence interval for the true mean age of oak trees.

Over the course of the school year, you keep track of how much snow falls on a given day and whether it was a snow day. your data indicates that of twenty-one days with less than three inches of snow, five were snow days, while of the eight days with more than three inches of snow, six were snow days. if all you know about a day is that it is snowing, what is the probability that it will be a snow day?