Number of plots 500 300 100 0+ 0 50 50 100 150 200 250 Number of trees
7.2.10 Researchers in the Hopkins Forest also count the number of maple trees (genus acer) in plots
throughout the forest. The following is a histogram of the number
of live maples in 1002 plots sampled over the past 20 years. The
average number of maples per plot was 19.86 trees with a standard
deviation of 23.65 trees.
a. If we took the mean of a sample of eight plots, what would
be the standard error of the mean?
b. Using the central limit theorem, what is the probability
that the mean of the eight would be within 1 standard error
of the mean?
c. Why might you think that the probability that you calculated in (b) might not be very accurate?
2. A normal population has mean 100 and variance 25.
How large must the random sample be if you want the standard
error of the sample average to be 1.5?
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