13. Excessive whaling in the 1900’s severely depleted the number of humpback whales. The worldwide population of humpback whales from 1900 to 1970 can be modeled by where P(t) is the humpback population and t is the years after 1900. Use this model to answer the questions below.
a. According to the model, how many humpback whales were alive in 1900?

b. According to the model, how many humpback whales were alive in 1920?

c. Use the model to graph the humpback whale population from 1930 to 1970.

17. a researcher measures three variables, x, y, and z for each individual in a sample of n = 20. the pearson correlations for this sample are rxy = 0.6, rxz = 0.4, and ryz = 0.7. a. find the partial correlation between x and y, holding z constant. b. find the partial correlation between x and z, holding y constant. (hint: simply switch the labels for the variables y and z to correspond with the labels in the equation.) gravetter, frederick j. statistics for the behavioral sciences (p. 526). cengage learning. kindle edition.