The time it takes a mechanic to change the oil in a car is exponentially distributed with a mean of 13 minutes a What is the probability density function for the time it takes to change the oil f x for x 0 b What is the probability that it will take a mechanic less than 14 minutes to change the oil Round your answer to four decimal places c What is the probability that it will take a mechanic between 11 and 13 minutes to change the oil Round your answer to four decimal places d What is the variance of the time it takes to change the oil