2002 AMC 8 Problem 20

Attempt Problem 20 of the 2002 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2002 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

20.

The area of triangle XYZXYZ is 88 square inches. Points AA and BB are midpoints of congruent segments XY‾\overline{XY} and XZ‾.\overline{XZ}. Altitude XC‾\overline{XC} bisects YZ‾.\overline{YZ}. The area (in square inches) of the shaded region is
1121 \frac{1}{2}
22
2122 \frac{1}{2}
33
3123 \frac{1}{2}
Answer: D
Concepts:similarityarea ratiomidpoint
Small hint:
The altitude splits the isosceles triangle into two equal halves.
Big hint:
The segment through the midpoints creates a similar triangle with half the side lengths.
Solution:
Since XY=XZXY=XZ and XCXC bisects YZ,YZ, altitude XCXC splits △XYZ\triangle XYZ into two congruent triangles. The left half △XYC\triangle XYC has area 4.4.
In △XYC,\triangle XYC, point AA is the midpoint of XY.XY. The horizontal segment through AA meets XCXC halfway up, so the small top triangle is similar to △XYC\triangle XYC with scale factor 12.\frac{1}{2}. Its area is therefore 14\frac{1}{4} of 4,4, or 1.1.
The shaded region is the rest of the left half, so its area is 4−1=3.4-1=3.
Thus, D is the correct answer.
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