Exponential Functions

Question

A radioactive substance is produced from nuclear fallout. if 600g of the substance decays to 250g in 20 years what is its half-life?

Answer 1

250 = 600e^20k

0.4167 ≈ e^20k

ln 0.4167 ≈ 20k

-0.8755 ≈ 20k

-0.0438 ≈ k

0.5 ≈ e^-0.0438t

ln 0.5 ≈ -0.0438t

15.8253 ≈ t