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szamy004 · Aug 26, 2009, 05:04 AM

hi can you please help me I have a few questions but this one is important

The quoted mean number of milligrams of sodium in a certain brand of low-salt microwave frozen dinners is 670mg. A random sample of 46 dinners is selected and found to have a mean of 685mg and standard deviation is 29mg.
a. Using the sample statistics, find a 90% confidence interval estimate of the true population mean number of milligrams of sodium in this brand of low-salt microwave frozen dinners.

I don't know how to work it out, and am getting confused with what formula to use.

help would be great please.

galactus · Aug 26, 2009, 03:48 PM

I will show you how to do this one. That way you will know how to do others. OK?

To find the maximum error of estimate, use the formula $E=z\cdot \frac{\sigma}{\sqrt{n}}$

Look up the z score for a 90% CI. It is 1.645.

$E=1.645\cdot \frac{29}{\sqrt{46}}=7.03$

Add this to and subtract from the sample mean $\overline{x}$

$685-7.03=677.97$

$685+7.03=692.03$

$677.07<{\mu}<692.03$

With 90% confidence, we can say that the mean sodium content of all dinners is between

677.97 and 692.03

That's all there is to it. OK now?

szamy004 · Aug 26, 2009, 05:09 PM

Thank you so much I have Been stressing all might about this I'll try the other questions and see how I go.
Again, thank you :-)