Let S be a sample of size 31 from a normally distributed population Omega . It is given that the average of the data in S is 120 and the standard deviation is 18. Construct a 90% confidence interval [a, b] for the population mean based on the data in the sample.

Acompany manufactures three types of cabinets. it makes 110 cabinets each week. in the first week, the sum of the number of type-1 cabinets and twice the number of type-2 cabinets produced was 10 more than the number of type-3 cabinets produced. the next week, the number of type-1 cabinets produced was three times more than in the first week, no type-2 cabinets were produced, and the number of type-3 cabinets produced was the same as in the previous week.