The weight of potato chips in a large​-size bag is stated to be 24 ounces. The amount that the packaging machine puts in these bags is believed to have a normal model with a mean of
24.4 ounces and a standard deviation of 0.22 ounces.
​a) What fraction of all bags sold are​ underweight?

​b) Some of the chips are sold in​ "bargain packs" of 3 bags.​ What's the probability that none of the 3 is​ underweight?

​c) What's the probability that the mean weight of the 3 bags is below the stated​ amount?

​d) What's the probability that the mean weight of a 20​-bag case of potato chips is below
24 ​ounces?