2002 Fermat Problem 17

The average age of a group of 140 people is 24. If the average age of the males in the group is 21 and the average age of the females is 28, how many females are in the group?

\textbf{(A)}\ 90\quad \textbf{(B)}\ 80\quad \textbf{(C)}\ 70\quad \textbf{(D)}\ 60\quad \textbf{(E)}\ 50

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