Question 5.5: Use the data in Example 5.4 to find an 80% confidence interv......

ISE Principles of Statistics for Engineers and Scientists [987713]

Use the data in Example 5.4 to find an 80% confidence interval.

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To find an 80% confidence interval, set 1 − 𝛼 = 0.80 to obtain 𝛼 = 0.20. Then look in the table for $z_{.10}$ , the $z$ -score that cuts off 10% of the area in the right-hand tail. The value is $z_{.10} = 1.28$ . So the 80% confidence interval is 408.20 ± (1.28)(8.7132). This can be written as 408.20 ± 11.15, or as (397.05, 419.35).

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