The map shows a top view of the Mississippi River. The gap between lines 1 and 2 shows how much Saint Anthony Falls receded betw
een 1680 and 1766. The gap between lines 3 and 4 shows how much the falls receded between 1856 and 1876. At what rate (on average) did the falls recede during each of these time spans? Express your answer in units of feet per year. Did the rate increase or decrease from one time span to the next? Hint: Determine how many years passed between lines 1 and 2 and between lines 3 and 4 to help you find your answers.
The time span between 1680 and 1766 (lines 1 and 2) is 86 years: 1766 − 1680 = 86 years. During this time, the falls receded an average of 5.8 feet per year: 500 feet ÷ 86 years ≈ 5.8 feet per year.
The time span between 1856 and 1876 (lines 3 and 4) is 20 years: 1876 − 1856 = 20 years. During this time, the falls receded an average of 25 feet per year: 500 feet ÷ 20 years = 25 feet per year.
The time span between 1680 and 1766 (lines 1 and 2) is 86 years: 1766 − 1680 = 86 years. During this time, the falls receded an average of 5.8 feet per year: 500 feet ÷ 86 years ≈ 5.8 feet per year.
The time span between 1856 and 1876 (lines 3 and 4) is 20 years: 1876 − 1856 = 20 years. During this time, the falls receded an average of 25 feet per year: 500 feet ÷ 20 years = 25 feet per year.
A. More food allows people to hunt more. B. More food allows the population to move from place to place. C. More food allows people to control their source of water. D. More food allows the population to grow.
