The amount of ${ }_{18}^{40} \mathrm{Ar}$ is one-ninth the amount of ${ }_{19}^{40} \mathrm{~K}$. If the half-life of the latter is $T$, what is the rock's age?
A) $T$
B) $T / 9$
C) $9 T$
D) $\ln (9 T)$
E) $T / \ln 9$
F) Some other result (specify)

Question

Quizplus · Accepted Answer

The rock's age is $T$ because the amount of ${ }_{19}^{40} \mathrm{~K}$ has decreased to half its original amount once, which corresponds to one half-life period $T$.

The Amount Of 1840Ar{ }_{18}^{40} \mathrm{Ar}1840​Ar Is One-Ninth the Amount Of 1940 K{ }_{19}^{40} \mathrm{~K}1940​ K

The Amount Of ${ }_{18}^{40} \mathrm{Ar}$ Is One-Ninth the Amount Of ${ }_{19}^{40} \mathrm{~K}$