「Answer」AMC8 -- 2000年真题解析( 三 ) |has|units|Area|

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Answer: B
Solution:
Let the sum of first 3 numbers is a, the fourth number is x, and the sum of last 3 numbers is c, then :a+x=5*4;x+b=8*4;a+x+b=7*(46/7);we get x=6 from the above 3 equations.Problem 24
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Answer: D
Solution:
<AFG=（180-<A）/2=80；thus , <BFD=180-<AFG=100;In Triangle BFD; <B+<D=180-<BFD=180-100=80.Problem 25

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Answer: B
Solution:
To quickly solve this multiple choice problem, make the (not necessarily valid, but very convenient) assumption that ABCD can have any dimension. Give the rectangle dimensions of AB=CD=12 and BC=AD=6, which is the easiest way to avoid fractions. Labelling the right midpoint as M, and the bottom midpoint as N, we know that DN=NC=6; BM=MC=3.Area(AND)=1/2*6*6=18; Area(MNC)=1/2*6*3=9; Area(ABM)=1/2*12*3=18; Area(AMN)=Area(ABCD)-Area(AND)-Area(MNC)-Area(ABM)=72-18-9-18=27.AMC培训、答疑，请联系微信 / 电话：136 1118 1627
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