The technique known as potassium-argon dating is used to date old lava flows and thus any fossilized skeletons found in them, like this 1.8-million-year-old hominid skull. The potassium isotope 40^K has a 1.28 billion year half-life and is naturally present at very low levels. 40^K decays by beta emission into the stable isotope 40^Ar. Argon is a gas, and there is no argon in flowing lava because the gas escapes. Once the lava solidifies, any argon produced in the decay of 40^Ar is trapped inside and cannot escape.
What is the age of a piece of solidified lava with a 40^Ar/ 40^K ratio of 0.11?