The weight of potato chips in a small​-size bag is stated to be 6 ounces. The amount that the packaging machine puts in these bags is believed to have a normal model with a mean of 6.1 ounces and a standard deviation of 0.07 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 30​-bag case of potato chips is below 6 ​ounces?