What is the half-life of the goo in minutes?

Question

At the beginning of an experiment, a scientist has 348 grams of radioactive goo. After 90 minutes, her sample has decayed to 10.875 grams.

A) What is the half-life of the goo in minutes?

B)Find a formula for , the amount of goo remaining at time . 

C)How many grams of goo will remain after 65 minutes? 

Answer 1

10.875 = 384 e^90k

0.02832 ≈ e^90k

ln 0.02832 ≈ 90k

-3.5648 ≈ 90k

-0.0396 ≈ k

0.5 ≈ e^-0.096t

ln 0.5 ≈ -0.096t

-0.6931 = -0.0396t

17.5 ≈ t