Two different cars each depreciate to 60% of their respective original values. The first car depreciates at an annual rate of 10%. The second car depreciates at an annual rate of 15%. What is the approximate difference in the ages of the two cars?

Question

1.7 ears
2.0 years
3.1 years
or 5.0 years

Answer 1

log_0.900.6 - log_0.850.6 = 1.7

or, since you probably don't have a button for log_0.9x,

log(0.6)/log(0.9) - log(0.6)/log(0.85)
or even
log(0.6)(1/log(0.9)-1/log(0.85))

Answer 2

Two different cars each depreciate to 60% of their respective original values. The first car depreciates at an annual rate of 10%. The second car depreciates at an annual rate of 15%. What is the approximate difference in the ages of the two cars?