Problem
1975 AHSME Problem 23
In the adjoining figure AB and BC are adjacent sides of square ABCD; M is the midpoint of AB; N is the midpoint of BC; and AN and CM intersect at O. The ratio of the area of AOCD to the area of ABCD is
![[asy] draw((0,0)--(2,0)--(2,2)--(0,2)--(0,0)--(2,1)--(2,2)--(1,0)); label("A", (0,0), S); label("B", (2,0), S); label("C", (2,2), N); label("D", (0,2), N); label("M", (1,0), S); label("N", (2,1), E); label("O", (1.2, .8)); [/asy]](/static/aops/31edb098b5398ce0cb0d5cf757b54a1f9fc36e72.png)
\textbf{(A)}\ \frac{5}{6}\qquad \textbf{(B)}\ \frac{3}{4}\qquad \textbf{(C)}\ \frac{2}{3}\qquad \textbf{(D)}\ \frac{\sqrt{3}}{2}\qquad \textbf{(E)}\ \frac{(\sqrt{3}-1)}{2}
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