Grace's entertainment expenses for the year were: $50 , $55 , $60 , $50 , $55 , $60 , $50 , $60 , $55 What is the standard deviation of her expenses? Use the following formula to calculate standard deviation: sigma is equal to square root of the fraction with numerator the sum from i is equal to 1 to n of open paren x sub i minus m close paren squared and denominator n end root where x sub i is each data point, and n is the number of data points.