X space plus-or-minus space Z space fraction numerator s over denominator square root of n end fraction Where: X is the mean Z is the Z-value from the table below S is the standard deviation N is the number of observations (sample size) Confidence Z constant value 80% 1.282 85% 1.440 90% 1.645 95% 1.960 99% 2.576 99.5% 2.807 99.9% 3.291 Calculate the confidence interval when X = 10 with a 90% confidence, a standard deviation of 2, and a sample size of 100