Chapter 21, Problem 39E

A sample of rock was found to contain 8.23 mg of rubidium-87 and 0.47 mg of strontium-87..

(a) Calculate the age of the rock if the half-life of the decay of rubidium by $\text{β}$ emission is $4.7\times {10}^{10}$ y.

(b) If some $\text{S}\text{r}$ was initially present in the rock, would the rock be younger, older, or the same age as the age calculated in (a)? Explain your answer.