Posted by **angel** on Wednesday, April 11, 2007 at 5:11pm.

The average time in data to process orders received by a metal fabrication company is to be estimated. A sample of

20 orders is randomly selected from a total of 200 orders processed over a

6 month period and the sample mean is

5.4 days with a standard deviation of 1.2 days. compute a 90 percent confidence interval of the estimated average processing time.

I know from my sheet that 90%= 1.64

please help

You have everything you need to calculate the confidence interval.

Formula:

CI90 = mean + or - 1.64 (sd/√n)

Using your data:

CI90 = 5.4 + or - 1.64 (1.2/√20)

Finish the calculation to determine the interval.

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