Understanding Basic Statistics 6th Edition by Charles Henry Brase,Corrinne Pellillo Brase

تمرين 104

Coal: Automatic Loader Coal is carried from a mine in West Virginia to a power plant in New York in hopper cars on a long train. The automatic hopper car loader is set to put 75 tons of coal into each car. The actual weights of coal loaded into each car are normally distributed, with mean = 75 tons and standard deviation = 0.8 ton.
(a) What is the probability that one car chosen at random will have less than 74.5 tons of coal
(b) What is the probability that 20 cars chosen at random will have a mean load weight
of less than 74.5 tons of coal
(c) Interpretation Suppose the weight of coal in one car was less than 74.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment Suppose the weight of coal in 20 cars selected at random had an average
of less than 74.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment Why