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.