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.
Q(t) = Q0 · 2-(t/140)

If the amount of polonium left after 280 days is 90 mg, what was the initial amount present?

Question

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.
Q(t) = Q0 · 2-(t/140)

If the amount of polonium left after 280 days is 90 mg, what was the initial amount present?

michele_laino · Answer

please you have to solve this equation:
$$90 = {Q_0} \cdot {2^{ - \left( {280/140} \right)}}$$
please what is Q_0?