Shown, again, in the following table is world population, in billions, for seven selected years from 1950 through 2010. Using a graphing utility’s logistic regression option, we obtain the equation shown on the screen.We see from the calculator screen at the bottom of the previous page that a logistic growth model for world population, f(x), in billions, x years after 1949 is

Use this function to solve Exercises 38–42.

When did world population reach 7 billion?

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.x, Number of Years after 1949 1 (1950) 11 (1960) 21 (1970) 31 (1980) 41 (1990) 51 (2000) 61 (2010) y, World Population (billions) 2.6 3.0 3.7 4.5 5.3 6.1 6.9