1. List all 36 gas prices in cells A1 to A36 in your excel spreadsheet. 2. Type =average (Al : A36) to find the sample mean 3. Type =stdev . s (A1 : A36) to find the sample standard deviation 4. Let's assume your sample mean is 3.65 with a std of 0.43. 5. Determine the Margin of Error (for 0.05 significance) by typing =confidence . norm ( . 05, . 43, 36) . This is your E value 6. Finally, compute the 95% Confidence Interval by adding and subtracting the Margin of ensor from your mean: =(3.65 + E) for the Upper bound and =(3.65 - E) for the Lower bound