Answer:
d. 4 years
Step-by-step explanation:
A graphing calculator can be a real help with problems like this.
Or, you can write an explicit formula for the population and solve for the time it takes.
p = p0(1 +r)^t = 20,000(0.91^t) . . . . . . for r = -0.09, p0 = 20,000
Fill in p=14000, and divide by 20,000.
14000/20000 = 0.91^t
Take logarithms.
log(14/20) = t·log(0.91)
log(0.7)/log(0.91) = t ≈ 3.782
In 4 years, the town's population will be fewer than 14,000.
