standard_description: Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm’s law V = IR to highlight resistance R.
problem_activity: Potassium-40 has a half-life of
$${1.28\times 10^9}$$
years, which means that after that many years, half of a sample has decayed into a different isotope of carbon. If a sample began with
$${115}$$
grams of potassium-40
$${30,000,000}$$
years ago, how much is left today? How long will it be until there are only
$${50}$$
grams remaining?


aligns: no