A. A manufacturer knows that their items have a normally distributed length, with a mean of 19.7 inches, and standard deviation of 4 inches.
If 25 items are chosen at random, what is the probability that their mean length is less than 17.4 inches?
Round to 4 decimal places
A manufacturer knows that their items have a normally distributed lifespan, with a mean of 12.1 years, and standard deviation of 1.9 years.
If you randomly purchase 12 items, what is the probability that their mean life will be longer than 11 years?
Round to 4 decimal places.
B. A company produces steel rods. The lengths of the steel rods are normally distributed with a mean of 98.4-cm and a standard deviation of 0.9-cm. For shipment, 15 steel rods are bundled together.
Find the probability that the average length of the rods in a randomly selected bundle is between 97.9-cm and 98.6-cm.
P(97.9-cm < X¯¯¯ < 98.6-cm) = Round to 4 decimal places.
