Ginny is studying a population of frogs. she determines that the population is decreasing at an average rate of 3% per year. when she began her study, the frog population was estimated at 1,200. which function represents the frog population after x years?

(1) f(x) = 1,200(1.03)^x
(2) f(x) = 1,200(0.03)^x
(3) f(x) = 1,200(0.97)^x
(4) f(x) = 1,200(0.97)^x

In the first year the population declines by 3%.  So the population at the end of the first year is the starting population (1200) minus the decline: 1200 minus 3% of 1200.  3% of 1200 is the same as .03 * 1200.  So the population at the end of the first year is 1200 - .03 * 1200.  That can be written as 1200 * (1 - .03), or 1200 * 0.97

What about the second year?  The population starts at 1200 * 0.97.  It declines by 3% again.  But 3% of what???  The decline is based on the population at the beginning of the year, NOT based no the original population.  So the decline in the second year is 0.03 * (1200 * 0.97).  And just as in the first year, the population at the end of the second year is the population at the beginning of the second year minus the decline in the second year.  So that's 1200 * 0.97 - 0.03 * (1200 * 0.97), which is equal to 1200 * 0.97 (1 - 0.03) = 1200 * 0.97 * 0.97 = 1200 * 0.972.

So there's a pattern.  If you worked out the third year, you'd see that the population ends up as 1200 * 0.973, and it would keep going like that.

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TheBlueFox

x=6 and x=3

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1 number

if we use a graphing calculator, there is only one such number that satisfies the conclusion of the mean value theorem, that is, a number such that

where the right-hand side is the average rate of change of f on the interval [0.5,0.75], which is the slope of the secant line.

in the attached graph, the black line is the secant line which has its slope as the average rate of change of f on [0.5,0.75], while the orange line is the only tangent line to the graph of f in the interval that satisfies the mvt conclusion.