Willows in Yellowstone Writers in some fields summarize data by giving x– and its standard error rather than x– and sx. Biologists studying willow plants in Yellowstone National Park reported their results in a table with columns labeled x– ± SE. The table entry for the heights of willow plants (in centimeters) in one region of the park was 61.55 ± 19.03.21 The researchers measured a total of 23 plants.

(a) Find the sample standard deviation sx for these measurements.

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(b) A hasty reader believes that the interval given in the table is a 95% confidence interval for the mean height of willow plants in this region of the park. Find the actual confidence level for the given interval.