Random sample of 120 customers’s spent an average of 9.2 hours on their professional job with a sample standard deviation of 5.1 hours. Calculate the specification hours with confidence of 95%.

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- December 15th 2008, 10:46 PMmagentaritaSpecification Hours
Random sample of 120 customers’s spent an average of 9.2 hours on their professional job with a sample standard deviation of 5.1 hours. Calculate the specification hours with confidence of 95%.

- December 17th 2008, 04:02 PMmeymathis
I have not heard of

*specification hours*. It looks like you are supposed to calculate the confidence interval with 95% confidence level.

The Central Limit Theorem (which the general rule of thumb says is ok to invoke for ) tells us that is approximately normally distributed with mean 0 and std dev 1.

So then the confidence interval is given by where is defined by (*Z*is from the standard normal distribution). I'm assuming that you have already seen where these formulas came from.

So from a standard normal distribution table . So just plug away. - December 21st 2008, 12:53 PMmagentaritaok...