The radioactive element polonium decays according to the law given below where Q0 is the initial amount and the time t is measured in days.

Question

Q(t) = Q0 · 2-(t/140)
If the amount of polonium left after 700 days is 45 mg, what was the initial amount present?
mg

Answer 1

Q0 2^-(700/140) = 45

Note that 700 days is 5 half-lives
So, 1/32 of Q0 is left

Q0 = 32*45 = 1440