Calculate the standard deviation of 2,3,3,4,5,5,7,7,9?

To calculate the standard deviation, we first need to find the mean of the data set:

(2 + 3 + 3 + 4 + 5 + 5 + 7 + 7 + 9) / 9 = 45 / 9 = 5

Next, we subtract the mean from each data point, square the result, and then find the average of those squared differences:

(2-5)^2 + (3-5)^2 + (3-5)^2 + (4-5)^2 + (5-5)^2 + (5-5)^2 + (7-5)^2 + (7-5)^2 + (9-5)^2
= 9 + 4 + 4 + 1 + 0 + 0 + 4 + 4 + 16
= 42

Now, we divide the sum of squared differences by the number of data points (9) and take the square root of the result to find the standard deviation:

√(42 / 9) = √4.6667 ≈ 2.16

Therefore, the standard deviation of the data set {2, 3, 3, 4, 5, 5, 7, 7, 9} is approximately 2.16.