2.31 Timber Tracts To estimate the amount of lumber in a tract of timber, an owner decided to count the number of trees with diameters exceeding 30 cm in randomly selected 15-by-15 m. Seventy 15-by-15 m were chosen, and the selected trees were counted in each tract. The data are listed here:

a. Construct a relative frequency histogram to describe the data.

b. Calculate the sample mean x as an estimate of u, the mean number of timber trees for all 15-by-15 m in the tract.

c. Calculate s for the data. Construct the intervals xs, x2s, and 3s. Calculate the percentage of squares falling into each of the three intervals, and compare with the corresponding percentages given by the Empirical Rule and Tchebysheff's Theorem.

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