If 11(0.9)^t gives the mass of radioactive material in grams as a function of time measured in days since the time the mass was 11 grams, what, accurate to the nearest thousandth, is the rate of change of the mass five days after the time the mass was 11 grams?
if f(t) = 11(0.9)^t then
f'(t) = 11 ln0.9 * 0.9^t
so plug in t=5