Simple algorithm using the big theta - notation

Sometimes a slight change in a problem can significantly alter the form of its solution.  For example, find a simple algorithm for solving the following problem and classify it using big-theta notation:

Divide a group of people into two disjoint subgroups (of arbitrary size) such that the difference in the total ages of the members of the two subgroups is as large as possible.
------------------
formular :- all algorithms whose graphs have a shape of parabola such as an insertion sort are classified in the class represented by (n^2) " read big-theta of n squared"

All algorithms whose graph have the shape of a logarithmic expression such as the binary search fall in the class represented by (lg n) "read big-theta of log n"