1. 2. Step 1. Given: X = , ta/2 = = ,n= Step 2. Solve: X t ta/2 (s/ Vn ) So, and Step 3. Therefore,1. Find the 95th percentile when of = 25. 2. City planners wish to estimate the mean lifetime of the most commonly planted trees in urban settings. A sample of 16 recently felled trees yielded a mean age of 33 years with a standard deviation of 3 years. Assuming that the lifetime of such trees are normally distributed, construct a 99% confidence interval for the mean lifetime of all trees