calculating age of rock sample I have the question: "If a rock has a parent:daughter isotope ratio of 1:10 and the parent isotope is Rb-87, given that the half-life of Rb-87 is 48800 x 10^6 years. Calculate the age of the rock sample. " here is my attempt is this correct ? Parent Isotope = 1 Daughter Isotope = 10 so, Number of left parent isotope/ number of net isotope initially = 1/11 = ln(2)/48.8*10^9 [ half life of the sample] so, t = 168.82*10^9 years Is this correct ?

Well, the equation for $t$ is $\large{\frac{1}{11}=2^{-\frac{t}{4.88 \cdot 10^{10}}}}$ or $\large{11=2^{\frac{t}{4.88 \cdot 10^{10}}}}$. Thus, $t=\frac{\ln 11}{\ln 2} \cdot 4.88 \cdot 10^{10} \approx 1.6882 \cdot 10^{11}$