As the individual responsible for determining demand forecasts for an item within an important product line, you always exceed your superior's expectations by providing a range in addition to a point estimate of demand. Most recently you determined your unbiased forecast of expected demand for next period to be 65.00 units. You informed your superior that the historical standard deviation of demand is 6.10 units so that a reasonable range within which actual demand will fall would have a lower limit of 55.00 units and an upper limit of 75.00 units. What size confidence interval were you using for this range?

Remember: Z=(x-μ)/σ