Omar recorded the number of hours he worked each week for a year. The random sample that he took from his data is given. 13 , 17 , 9 , 21 What is the standard deviation for the data? Standard deviation: s=sqrt(((x_1−x―)^2+(x_2−x―)^2+...+(x_n−x―)^2)/(n−1))

The mean of 13, 17, 9, and 21 is 15. The squared differences from the mean add to 4 + 4 + 36 + 36 = 80; divide by n − 1 = 3 and take the square root: √(80/3) ≈ 5.2. The standard deviation is 5.2, choice B.

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