A manager has been using a certain technique to forecast demand for gallons of ice cream for the past six periods. Actual and forecasted amounts are shown below. Period Demand Forecast 1 90 87 2 85 88 3 91 87 4 92 89 5 95 90 6 88 92 What is the sigma (or standard deviation) for this forecasting technique? a. 1.099 b. 3.074 c. 2.067 d. 4.099 e. None of the other options are correct