Consider the following data set with a mean of 12: 9, 11, 12, 16 Using the equation below or the standard deviation formula in Excel, calculate the standard deviation for this data set. Answer choices are rounded to the hundredths place. s equals square root of fraction numerator 1 over denominator n minus 1 end fraction sum from i equals 1 to n of open parentheses X subscript i minus X with bar on top close parentheses squared end root a.) 2.94 b.) 1.54 c.) 5.09 d.) 2.55