A Jiffy Lube franchise manager is concerned about the amount of time it takes for his technicians to change the oil and filters of cars. The current mean time for the complete operation is 18 minutes. He hasn’t kept track of the number of times his employees took more than 30 minutes to complete a car but he knows that the probability is too high. There are several ways to reduce the mean time. Determine the mean time necessary to reduce the probability that a job takes longer than 30 minutes to 10%.