Radio Active Decay Problem?

Question

Okay here is the problem...

The equation A=Aoe^-0.000124t determines the decay of carbon-14. Find the age of a sample in which has 92% of the original radioactive nuclei are still present.

Ao=original amount
t=time


THANKS FOR HELPING!

Answer 1

If the sample has 92 percent of the original radioactive nuclei, then A = .92Ao.
A=Aoe^-0.000124t

Substitute A:
.92Ao = Aoe^-0.000124t

Divide by Ao:
.92 = e^-0.000124t

Natural log of both sides:
ln .92 = -0.000124t
-0.08338 = -0.000124t

Divide both sides by -0.000124:
-0.08338/-0.000124 = t
t = 672.42 years