Suppose the Ratio of Radiogenic ⁴⁰K to Nonradiogenic ³⁹K Was

Multiple Choice

Suppose the ratio of radiogenic ⁴⁰K to nonradiogenic ³⁹K was 1:10 at the time a rock was formed, and that at that time also the ratio between radiogenic ⁴⁰Ar to ³⁹K was 1:20. Now, when the rock is analyzed, it is found that the ratios are ⁴⁰K/³⁹K = 1:20 and ⁴⁰Ar/³⁹K = 1:10. How old is the rock (in billions of years) ?

A) 0.13
B) 1.3
C) 13
D) 26