statistics
posted by Anonymous .
A provincial politician would like to determine the average amount earned during summer employment by the provinces teenagers during the past summer’s vacation period. She wants to have 95% confidence that the sample mean is within $25 of the actual population mean. Bases on past studies, she knows the amount earned is normally distributed with a standard deviation of $400. What sample size must she take?

95% = mean ± 1.96 SEm
SEm = SD/√n
25 = 1.96 (400/√n)
Calculate n.