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2012 AMC 10B Problem 19

Problem 19 of 25HarderGeometry

In rectangle ABCD,ABCD, AB=6,AB=6, AD=30,AD=30, and GG is the midpoint of AD.\overline{AD}. Segment ABAB is extended 22 units beyond BB to point E,E, and FF is the intersection of ED\overline{ED} and BC.\overline{BC}. What is the area of quadrilateral BFDG?BFDG?

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Solution

The polygon BFDGBFDG is a trapezoid with bases DGDG and BFBF and height 6.6. Also, since GG is the midpoint between AA and D,D, we have GD=15.GD= 15. We can see that EBFEAD,EBF \sim EAD , so BFAD=EBEA\dfrac{BF}{AD} = \dfrac{EB}{EA} BF30=28\dfrac{BF}{30} = \dfrac 28 BF=7.5BF = 7.5 This makes the area of BFDGBFDG equal to 6(15+7.5)2=1352.\dfrac{6(15+7.5)}2 = \dfrac{135}2. Thus, the correct answer is C .

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Concepts: similarity · trapezoid · area

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.