AoPSWiki
Our Precalculus course starts on Dec. 4. Master trig, complex numbers, and vectors and matrices in 2 and 3 dimensions. Click here to enroll today!

University of South Carolina High School Math Contest/1993 Exam/Problem 16

From AoPSWiki

Problem

In the triangle below, \displaystyle M, N, and P are the midpoints of BC, AB, and AC respectively. CN and AM intersect at O. If the length of CQ is 4, then what is the length of OQ?

Image:Usc93.16.PNG
\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }4/3 \qquad \mathrm{(C) \ }\sqrt{2} \qquad \mathrm{(D) \ }3/2 \qquad \mathrm{(E) \ }2

Solution

AM and CN are the medians of \triangle ABC, so their intersection point O is the centroid of the triangle. Also, \frac{CM}{MB} = \frac{CP}{PA} = 1 so MP is parallel to AB and thus \frac{CQ}{QN} = 1 and CQ = QN = 4. Then CN = CQ + QN = 8. Since the centroid trisects the medians, CO = \frac23 CN = \frac{16}3 and OQ = CO - CQ = \frac{16}3 - 4 = \frac43 which is answer choice \mathrm{(B)}.



Try our innovative online adaptive learning system, Alcumus.
Over 1100 problems and 60+ video lessons. FREE!
© Copyright 2008 AoPS Incorporated. All Rights Reserved. • FoundationPrivacyContact Us