In the steel manufacturing process, the number of checking defects on 20 billet products are as follows: 4,0,2, 5, 7,4, 2, 4,4, 2,4, 7, 1,2, 3, 4, 7, 2,4,2 (a) What distribution is suitable for describe the number of checking defects in every product? (b) Based on your answer in (a), what is the condence interval of the expected number of checking for each product? (Here, we assume that a = 0.05) Hint: Poisson process can be approximated as a normal distribution (the mean should be calculated from the given data)