Question

200 mg of a radioactive substance decays at a rate of 5% per day.

A) Write an equation that models the mass (M) as a function of t (time in days).
M(t)=______

B) What will be the mass of the substance after 10 days?

C) How long will it take for the radioactive substance to decay to 5rg?

Answer 1

M(t) = 200 (.95)^t, where t is the number of days

B) when t = 10
M(10) = 200(.95)^10 = .....

c) when is M(t) = 5 ???
200(.95)^t = 5
.95^t = .025
t log .95 = log .025
t = log .025/log .95 = .....