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**jsu03** A chemist obtained the following data for the alcohol content of a sample of blood: 0.084, 0.089, 0.079. Cal the mean and 95% confidence limits. How many more measurements would be needed to lower the uncertainty to +/- .008.

I already did the calulations n got: Mean = 0.084, standard value = 5.0 * 10^-3 and for 95% confidence limits, the answer is 0.084 +/- 0.015. The part how many more measurements would be needed .... is where I am stuck on. Can someone help me please. I need the formula for n. Thanks inadvance!!