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Difference between revisions of "1975 AHSME Problems/Problem 28"

(Created page with "==Solution== Here, we use Mass Points. Let <math>AF = x</math>. We then have <math>AE = 2x</math>, <math>EC = 16-2x</math>, and <math>FB = 12 - x</math> Let <math>B</math> hav...")
 
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== Problem 28 ==
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In <math>\triangle ABC</math> shown in the adjoining figure, <math>M</math> is the midpoint of side <math>BC, AB=12</math> and <math>AC=16</math>. Points <math>E</math> and <math>F</math> are taken on <math>AC</math>
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and <math>AB</math>, respectively, and lines <math>EF</math> and <math>AM</math> intersect at <math>G</math>. If <math>AE=2AF</math> then <math>\frac{EG}{GF}</math> equals
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<asy>
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draw((0,0)--(12,0)--(14,7.75)--(0,0));
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draw((0,0)--(13,3.875));
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draw((5,0)--(8.75,4.84));
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label("A", (0,0), S);
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label("B", (12,0), S);
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label("C", (14,7.75), E);
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label("E", (8.75,4.84), N);
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label("F", (5,0), S);
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label("M", (13,3.875), E);
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label("G", (7,1));
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</asy>
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<math>\textbf{(A)}\ \frac{3}{2} \qquad
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\textbf{(B)}\ \frac{4}{3} \qquad
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\textbf{(C)}\ \frac{5}{4} \qquad
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\textbf{(D)}\ \frac{6}{5}\\ \qquad
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\textbf{(E)}\ \text{not enough information to solve the problem} </math>
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==Solution==
 
==Solution==
 
Here, we use Mass Points.
 
Here, we use Mass Points.
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~JustinLee2017
 
~JustinLee2017
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==See Also==
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{{AHSME box|year=1975|num-b=27|num-a=29}}
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{{MAA Notice}}

Revision as of 22:27, 12 February 2021

Problem 28

In $\triangle ABC$ shown in the adjoining figure, $M$ is the midpoint of side $BC, AB=12$ and $AC=16$. Points $E$ and $F$ are taken on $AC$ and $AB$, respectively, and lines $EF$ and $AM$ intersect at $G$. If $AE=2AF$ then $\frac{EG}{GF}$ equals

[asy] draw((0,0)--(12,0)--(14,7.75)--(0,0)); draw((0,0)--(13,3.875)); draw((5,0)--(8.75,4.84)); label("A", (0,0), S); label("B", (12,0), S); label("C", (14,7.75), E); label("E", (8.75,4.84), N); label("F", (5,0), S); label("M", (13,3.875), E); label("G", (7,1)); [/asy]

$\textbf{(A)}\ \frac{3}{2} \qquad \textbf{(B)}\ \frac{4}{3} \qquad \textbf{(C)}\ \frac{5}{4} \qquad \textbf{(D)}\ \frac{6}{5}\\ \qquad \textbf{(E)}\ \text{not enough information to solve the problem}$

Solution

Here, we use Mass Points. Let $AF = x$. We then have $AE = 2x$, $EC = 16-2x$, and $FB = 12 - x$ Let $B$ have a mass of $2$. Since $M$ is the midpoint, $C$ also has a mass of $2$. Looking at segment $AB$, we have \[2 \cdot (12-x) = \text{m}A_{AB} \cdot x\] So \[\text{m}A_{AB} = \frac{24-2x}{x}\] Looking at segment $AC$,we have \[2 \cdot (16-2x) = \text{m}A_{AC} \cdot 2x\] So \[\text{m}A_{AC} = \frac{16-2x}{x}\] From this, we get \[\text{m}E = \frac{16-2x}{x} + 2 \Rrightarrow \text{m}E = \frac{16}{x}\] and \[\text{m}F = \frac{24-2x}{x} + 2 \Rrightarrow \text{m}F = \frac{24}{x}\] We want the value of $\frac{EG}{GF}$. This can be written as \[\frac{EG}{GF} = \frac{\text{m}F}{\text{m}E}\] Thus \[\frac{\text{m}F}{\text{m}E} = \frac {\frac{24}{x}}{\frac{16}{x}} = \frac{3}{2}\] $\boxed{A}$

~JustinLee2017

See Also

1975 AHSME (Problems • Answer Key • Resources)
Preceded by
Problem 27 		Followed by
Problem 29
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 • 26 • 27 • 28 • 29 • 30
All AHSME Problems and Solutions

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