A processing company wants to ensure that the taste of its very popular frozen low-fat diner meets the six Sigma quality standards. The manufacturing engineers believe that the taste is strongly related to the percentage of the secret spice (known as Alpha-Omega 1001) that is added during the production process. A number of consumers taste tests were conducted and it was found that all samples that were rated excellent contained between 1.5 and 3.25 percentage Alpha-Omega 1001, calculate the standard deviation necessary to achieve Six Sigma quality.