Because the question asks for the sample standard deviation, use this formula: s = square root of (sum of x - xBar)² / (n - 1) There are 9 numbers, there, so n - 1 = 8 Next, find the mean (xBar): 15 + 42 + 53 + . . . + 47 = 227. 227 / 9 = ~25.2 Next, for each number, subtract xBar and square the result, like this: (15 - 25.2)² = 104.0 (42 - 25.2)² = 282.2 (53 - 25.2)² = 772.8 ... Next, add up all those values (i.e., 104 + 282.2 + 772.8...) and divide by (n - 1). In this example, the answer to this is 2,535.2 / 8, or 316.9. Finally, take the square root of that number to get s. sqrt (316.9) = 17.8. Therefore, the answer is 17.8.