Chapter 3 - Section 3.5 - Exponential Growth and Decay; Modeling Data - Exercise Set - Page 506: 19

Age of paintings: about 15,679 years

Model: $ A=A_{0}e^{-0.000121t}$ Unknown: $ t $, when $ A=0.15A_{0},$ $0.15A_{0}=A_{0}e^{-0.000121t}\qquad... /\div A_{0}$ $0.15=e^{-0.000121t}\qquad.../\ln(...)$ $-1.89712=-0.000121t\qquad.../\div(-0.000121)$ $ t\approx 15678.67$ Age of paintings: about 15,679 years