The time needed to complete one test has been found to be normally distributed with a mean of 30 minutes and a standard deviation of 10 minutes....

 The time needed to complete one test has been found to be normally distributed with a mean of 30 minutes and a standard deviation of 10 minutes. (NOTE: you must first define a random variable .) (a) What is the probability of completing the test in more than 20 minutes but less than 40 minutes? (b) If the probability of completing the test in T minutes or less is 0.8, find T

Question 9. Twenty percent of all cars manufactured by a certain company have