1954 AHSME Problem 23

If the margin made on an article costing C dollars and selling for S dollars is M=\frac{1}{n}C, then the margin is given by:

\begin{array}{l} \textbf{(A)}\ M=\frac{1}{n-1}S\qquad\textbf{(B)}\ M=\frac{1}{n}S\qquad\textbf{(C)}\ M=\frac{n}{n+1}S\\ \textbf{(D)}\ M=\frac{1}{n+1}S\qquad\textbf{(E)}\ M=\frac{n}{n-1}S \end{array}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.