The decay of 243 mg of an isotope is given by $$\mathrm { A } ( \mathrm { t } ) = 243 \mathrm { e } ^ { - 0.014 \mathrm { t } }$$ where t is time in years since the initial amount of 243 mg was present. Find the amount (to the nearest milligram) left after 72 years.
A) 240
B) 89
C) 45
D) 87

Question

Quizplus · Accepted Answer

The amount left after 72 years is $$243 \mathrm { e } ^ { - 0.014 	imes 72 } = 243 \mathrm { e } ^ { - 1.008 } = 89.08 \approx 89 \mathrm { mg }$$

The Decay of 243 Mg of an Isotope Is Given A(t)=243e−0.014t\mathrm { A } ( \mathrm { t } ) = 243 \mathrm { e } ^ { - 0.014 \mathrm { t } }A(t)=243e−0.014t

The Decay of 243 Mg of an Isotope Is Given $\mathrm { A } ( \mathrm { t } ) = 243 \mathrm { e } ^ { - 0.014 \mathrm { t } }$