**Questions:**

1) Strontium-90 has a decay constant of 0.024 y^{-1}. Determine the proportion of a strontium-90 sample which would remain after 50 years.

2) A sample initially contains 100,000 fluorine-20 atoms. Considering that fluorine-20 has a decay constant of 0.063 s^{-1}, determine how many F-20 atoms would remain after one minute.

3) Bromine-77 has a half life of 2.38 days. Determine the decay constant for Br-77.

4) A sample contains an unknown element. Initially, there is 80g of the unknown element, although after 3 days on 20g remain. Determine the decay constant of the element.

5) Lead-193 has a half life of 5s. Predict what proportion of a Pb-193 sample would remain after 12s.

6) Consider the graph below.

a) Using the graph determine the decay constant of the unknown element.

b) At what time would exact 200 atoms remain?