First off there are some issues in your questions but I can still help in answering this type of problem. First, there is no Sr-20. The 4 abundant form includes Sr-84, Sr-88, Sr-87, Sr-86, Sr-84. More importantly, the half life of strontium must be given.
For demonstration sake, let us assume Sr-85 is the isotope. It has a half-life of 64.853 days and I'm assuming the units of 87.3 is in days.
A/Ao = e^-(ln2/t)T
where A- final amount Ao -initial amount t- halflife T-total time elapsed
% = <span>e^-(ln2/64.853)(87.3) = 0.3933 or 39.33% </span><span> </span>
Darwin had arrived at a complete theory of evolution by 1839, but it was to be another 20 years before he published his ideas of evolution through natural selection in his epochal book On the Origin of Species by Means of Natural Selection.
