Six Sigma quality (3.4 defects per million units produced) is probably a bit much to ask of Rachel's old oven.
a. What would the standard deviation in the temperature of her oven need to be if she settled for a "Three Sigma" level of quality?
b. If her oven exactly meets this quality level, what percentage of the time would her oven be operating at a temperature outside the acceptable range? (Hint: see Table 6-5.)