Question

A certain radioactive material is known to decay at a rate proportional to the amount present. A block of this material originally having a mass of 100 grams is observed after 20 years to have a mass of only 80 grams. Find the half-life of this radioactive material. (Recall that the half-life is the length of time required for the material to be reduced by a half.) (see attachment)

Answer 1

Assuming that it decays exponentially I got answer D, do you need some working?

Answer 2

nope

Answer 3

I got it right, thanks!