Suppose that a SRS of 900 12th-graders has x̅ =148. Based on this sample, a 95% confidence interval for μ is? (σ=35)

Question

I tried using x̅ +/- z*(σ/sqrt n), so 148 +/- 1.960(35/sqrt900, but it doesn't work. What am I doing wrong?

Answer 1

95% = 148 ± 1.96 (35/30) =148 ± 1.96(1.17) =

148 ± 2.287 = 145.713, 150.287

Is that what you calculated?