The shape of the distribution of the time required to get an oil change at a 20-minute oil-change facility is unknown. However, records indicate that the mean time is 21.1 minutes, and the standard deviation is 3.6 minutes. Complete parts (a) through (6) below. Click here to view the standard normal distribution table (page 1); Click here to view the standard normal distribution table (page 2); ...) D. The normal model cannot be used if the shape of the distribution is unknown. (b) What is the probability that a random sample of n = 40 oil changes results in a sample mean time less than 20 minutes? The probability is approximately I]. (Round to four decimal places as needed.)