At the end of each year, the Harcar Corporation assigns a rating to each member of its sales staff. The sales ratings are based on the mean (μ) and standard deviation (σ)for the individual sales totals for the year. The rating is computed by applying the following formula and then rounding the result to the nearest integer.

Individual rating = individual total−μ / σ

Sales staff are considered for promotion if their rating is 3. The graph shows the ratings for the entire sales staff for the years 2009, 2010, and 2011.