Critical values for quick reference during this activity. Condence level Critical value 0.90 2* = 1.645 0.95 z* : 1.960 The manager of a bookstore with a coffee shop wants to know the proportion of customers that come into :he store because of the coffee shop. A random sample of 75 customers was polled Use Sheet 1 of the Excel le linked above to calculate}?! and the 95% confidence interval. 15 = Ex: 1.234 Upper bound for 95% confidence interval = Ex: 1234 Lower bound for 95% condence interval = The manager can say with 95% confidence that the true population proportion of the customers that come into the store because of the coffee shop is in the interval [ Ex: 1.234 , ]