ACT Math · Exponential and logarithmic functions

A population model is given by P(t) = 500(1.08)^t, where t is measured in years. Which value is closest to P(5)?

A population model is given by P(t)=500(1.08)tP(t) = 500(1.08)^t, where tt is measured in years. Which value is closest to P(5)P(5)?

Answer and explanation

Answer: H: 735

Substitute t=5t=5 into the model: P(5)=500(1.08)5P(5)=500(1.08)^5. Since 1.082=1.16641.08^2=1.1664 and 1.084≈1.36051.08^4\approx1.3605, we get 1.085≈1.46931.08^5\approx1.4693, so P(5)≈500(1.4693)≈734.7P(5)\approx500(1.4693)\approx734.7, which is closest to 735735, choice H. Choice F (540540) applies the 8\% growth once, 500(1.08)500(1.08), instead of raising the growth factor to the 5th power. Choice G (700700) uses simple growth, 500(1+5⋅0.08)=700500(1+5\cdot0.08)=700, which ignores compounding. Choice J (800800) is too large; it would need a yearly growth factor close to 1.121.12. Exponential growth compounds each year on the larger amount.

More Exponential and logarithmic functions questions

All Exponential and logarithmic functions questions

Learn the method behind questions like this one

The ACT Math course teaches each tested skill through lessons, step-by-step solutions to sample problems, the complete study guide and full-length practice tests.