The decay of 242 mg of an isotope is given by A(t) = 242e....

Question

The decay of 242 mg of an isotope is given by A(t) = 242e^-0.017t, where t is time in years. Find the amount left after 72 years.

Please help! I missed 3 months of school because of health problems and can't figure a few problems out... I'm usually a straight A student, but have no idea what I am doing!

Answer 1

A(t) represents the amount of material remaining after time (t).

The decay formula is A(t) = 242e^-0.017t or 242 times e raised to the negative power 0.017 times t.

(t) is 72 years so the amount of the isotope remaining after 72 years is:

A(t) = 242 x e^{(-0.017 x 72)} = 242 x 0.294051605 = 71.16 mg