8. (a) In a survey conducted by a mail order company a random sample of 200 customers yielded 172 who indicated that they were highly satisfied with the delivery time of their orders. Calculate an...

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Extracted text: 8. (a) In a survey conducted by a mail order company a random sample of 200 customers yielded 172 who indicated that they were highly satisfied with the delivery time of their orders. Calculate an approximate 95% confidence interval for the proportion of the company's customers who are highly satisfied with delivery times. (b) A random sample of size 49 from a normal distribution gives a 99% confidence in- terval for the population mean as (30, 50). Find a 90% confidence interval for the population mean based on this information.