You calculate sample size using a standard deviation of 5, error of 1.5, and confidence level of 90%. Here is your calculation. Did you make an error? sample size = 1.644853627 *5 /1.5^2 = 3.655 You round to 4.0 Black starBlack starBlack star Marks possible: 1 (id #128) You forgot to use the power of 2, a common mistake. You used the wrong formula, you need the sample size proportion formula Brackets are missing so your exponent is applied to only the error. You make a rounding mistake. There is no error. You calculated it correctly