AP Chemistry

priscilla98

1. The problem statement, all variables and given/known data

Potassium-40 decays to Argon-40 within a half-life of 1.27 x 10^ 9 yr. What is the age of a rock in which the mass ration of 40 Ar to 40 K is 3.6?

2. Relevant equations

t 1/2 = .693 / k

3. The attempt at a solution

k = .693 / 1.27 x 10^-10 yr. ^-1

But I'm confused with the ratio, since they only give you one number. Would you use ln ( No/ Nt ) = kt