Two-sided Confidence Intervals

The two-sided $100\cdot(1-\alpha)\%$ confidence interval is centered at $\overline{x}$ and has upper and lower limits given by:

   upper limit$$\;=\;\overline{x}+z_{\alpha/2}\cdot\frac{\sigma}{\sqrt{n}}$$   Cell B14

   lower limit$$\;=\;\overline{x}-z_{\alpha/2}\cdot\frac{\sigma}{\sqrt{n}}$$   Cell B16