Suppose that Felisha is a librarian, and she read in a scholarly journal that the number of words in children's picture books published since 1950 is normally distributed with a mean of 802.2 words and a standard deviation of 92.0 words. She wishes to construct a confidence interval for the mean number of words in all children's picture books published after 2010, in case the number has changed in recent years. Felisha took a random sample of 20 children's picture books published after 2010 and counted the number of words in all 20 books. Her data is presented in the stem-and-leaf plot. 4 9
5 1 9
6 0 4 5
7 0 3 4 6 8
8 1 3 4 6
9 1 5 9
10 1 7
Leaf Unit = 10 Felisha calculated the mean of her sample to be 773.0 words, and now she wants to calculate the margin of error of a 99% confidence interval for the mean number of words in all books published after 2010. She assumes that the number of words in children's picture books published after 2010 has the same normal distribution and same standard deviation as the gencral population of all books published since 1950.