An unstable isotope we will call A has a half-life of 40,000 years and decays to a stable isotope we will call B. A mineral forms from a magma and becomes part of an igneous rock.
Initially, it contains no B atoms. A geologist analyzes the mineral and finds a ratio of atoms of
A to atoms of B of 1:7. Assuming no leakage in the environment, how old is the mineral?