Difference between revisions of "2010 AMC 12A Problems/Problem 3"
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− | == Problem | + | SCRIPT PREVIEW BY AZJPS |
+ | WILL AUTO-SUBMIT UNLESS YOU MOVE FROM WINDOW | ||
+ | == Problem == | ||
Rectangle <math>ABCD</math>, pictured below, shares <math>50\%</math> of its area with square <math>EFGH</math>. Square <math>EFGH</math> shares <math>20\%</math> of its area with rectangle <math>ABCD</math>. What is <math>\frac{AB}{AD}</math>? | Rectangle <math>ABCD</math>, pictured below, shares <math>50\%</math> of its area with square <math>EFGH</math>. Square <math>EFGH</math> shares <math>20\%</math> of its area with rectangle <math>ABCD</math>. What is <math>\frac{AB}{AD}</math>? | ||
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label("$H$",(0,0),SW); | label("$H$",(0,0),SW); | ||
</asy></center> | </asy></center> | ||
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<math>\textbf{(A)}\ 4 \qquad \textbf{(B)}\ 5 \qquad \textbf{(C)}\ 6 \qquad \textbf{(D)}\ 8 \qquad \textbf{(E)}\ 10</math> | <math>\textbf{(A)}\ 4 \qquad \textbf{(B)}\ 5 \qquad \textbf{(C)}\ 6 \qquad \textbf{(D)}\ 8 \qquad \textbf{(E)}\ 10</math> | ||
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Let <math>EF = FG = GF = HE = s</math>, let <math>AD = BC = h</math>, and let <math>AB = CD = x</math>. | Let <math>EF = FG = GF = HE = s</math>, let <math>AD = BC = h</math>, and let <math>AB = CD = x</math>. | ||
− | + | <cmath>\begin{align*}&0.2 \cdot s^2 = hs\\ | |
− | < | + | &s = 5h\\ |
− | + | &0.5 \cdot hx = hs\\ | |
− | + | &x = 2s = 10h\\ | |
− | + | &\frac{AB}{AD} = \frac{x}{h} = \boxed{10\ \textbf{(E)}}\end{align*}</cmath> | |
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=== Solution 2 === | === Solution 2 === | ||
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This helps us to see that <math>AD=a/5</math> and <math>AB=2a</math>, where <math>a=EF</math>. | This helps us to see that <math>AD=a/5</math> and <math>AB=2a</math>, where <math>a=EF</math>. | ||
Hence <math>\dfrac{AB}{AD}=\dfrac{2a}{a/5}=10</math>. | Hence <math>\dfrac{AB}{AD}=\dfrac{2a}{a/5}=10</math>. | ||
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+ | == See also == | ||
+ | {{AMC12 box|year=2010|num-b=2|num-a=4|ab=A}} | ||
+ | |||
+ | [[Category:Introductory Geometry Problems]] |
Revision as of 21:45, 25 February 2010
SCRIPT PREVIEW BY AZJPS WILL AUTO-SUBMIT UNLESS YOU MOVE FROM WINDOW
Problem
Rectangle , pictured below, shares of its area with square . Square shares of its area with rectangle . What is ?
Solution
Solution 1
Let , let , and let .
Solution 2
The answer does not change if we shift to coincide with , and add new horizontal lines to divide into five equal parts:
This helps us to see that and , where . Hence .
See also
2010 AMC 12A (Problems • Answer Key • Resources) | |
Preceded by Problem 2 |
Followed by Problem 4 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |