To study the output of a machine that fills boxes with cereal, a quality control engineer weighed 150 boxes of Brand X cereal. The frequency distribution in the following table summarizes his findings. Find the standard deviation of the weight of the boxes of cereal. (Round your answer to three decimal places.) Incorrect: Your answer is incorrect.
oz
x = Weight
(ounces) Number of
boxes
15.3 ≤ x < 15.6 14
15.6 ≤ x < 15.9 25
15.9 ≤ x < 16.2 84
16.2 ≤ x < 16.5 18
16.5 ≤ x < 16.8 9