Question

A paleontologist estimates that when a particular rock formed, it contained 12 mg of the radioactive isotope potassium-40. The rock now contains 3 mg of potassium-40. The half-life of potassium-40 is 1.3 billion years. About how old is the rock?

Answer 1

2.6 billion yrs old

Step-by-step explanation:

3 = 12 (1/2)^n n=2 half lives

2 * 1.3 bln = 2.6 bln