Suppose the Ratio of Radiogenic ²³⁸U to Nonradiogenic ²⁰⁴Pb Was

Multiple Choice

Suppose the ratio of radiogenic ²³⁸U to nonradiogenic ²⁰⁴Pb was 4:100 at the time a rock was formed, and also that at that time, the ratio of radiogenic ²⁰⁶Pb to ²⁰⁴Pb was 1:100. Now, when the rock is analyzed, it is found that the ratios are ²³⁸U/²⁰⁴Pb = 1:100 and ²⁰⁶Pb/²⁰⁴Pb = 4:100. How old is the rock (in billions of years) ?

A) 2.25
B) 4.5 b
C) 9
D) 13.5