How is the C.I. constructed when it is inverted to get back theta?

A random sample of pilots were tested in a ight simulator and the time for each to complete a certain corrective action was measured in seconds. Let X1, X2, . . . , Xn be the completion times and suppose they represent a random sample from an exponential population with parameter 3, given by 1 1 at; 9):???1 rial] and 9}{] {a} Derive a 95% condence interval for 9 based on the sufcient statisticJ Iii = 211:1 Xi. That is, nd a pivot based on 221:1 Xi and construct an appropriate probability statment that you can invert to nd a probability statement about 5'. ion in this context