Difference between revisions of "1967 AHSME Problems/Problem 9"

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\textbf{(B)}\ K \; \text{must be a rational fraction} \\
 
\textbf{(B)}\ K \; \text{must be a rational fraction} \\
 
\textbf{(C)}\ K \; \text{must be an irrational number} \qquad
 
\textbf{(C)}\ K \; \text{must be an irrational number} \qquad
\textbf{(D)}\ K\;  \text{must be an integer or a rational fraction} \qquad</math>
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\textbf{(D)}\ K \;  \text{must be an integer or a rational fraction} \qquad</math>
 
<math>\textbf{(E)}\ \text{taken alone neither} \; \textbf{(A)} \; \text{nor} \; \textbf{(B)} \; \text{nor} \; \textbf{(C)} \; \text{nor} \; \textbf{(D)} \; \text{is true}</math>
 
<math>\textbf{(E)}\ \text{taken alone neither} \; \textbf{(A)} \; \text{nor} \; \textbf{(B)} \; \text{nor} \; \textbf{(C)} \; \text{nor} \; \textbf{(D)} \; \text{is true}</math>
  
  
 
== Solution ==
 
== Solution ==
<math>\fbox{E}</math>
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From the problem we can set the altitude equal to <math>a</math>, the shorter base equal to <math>a-d</math>, and the longer base equal to <math>a+d</math>. By the formula for the area of a trapezoid, we have <math>K=a^2</math>. However, since <math>a</math> can equal any real number <math>(3, 2.7, \pi)</math>, none of the statements <math>A, B, C, D</math> need to be true, so the answer is <math>\fbox{E}</math>.
  
 
== See also ==
 
== See also ==
{{AHSME box|year=1967|num-b=8|num-a=10}}   
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{{AHSME 40p box|year=1967|num-b=8|num-a=10}}   
  
 
[[Category:Introductory Geometry Problems]]
 
[[Category:Introductory Geometry Problems]]
 
{{MAA Notice}}
 
{{MAA Notice}}

Latest revision as of 00:36, 16 August 2023

Problem

Let $K$, in square units, be the area of a trapezoid such that the shorter base, the altitude, and the longer base, in that order, are in arithmetic progression. Then:

$\textbf{(A)}\ K \; \text{must be an integer} \qquad \textbf{(B)}\ K \; \text{must be a rational fraction} \\ \textbf{(C)}\ K \; \text{must be an irrational number} \qquad \textbf{(D)}\ K \;  \text{must be an integer or a rational fraction} \qquad$ $\textbf{(E)}\ \text{taken alone neither} \; \textbf{(A)} \; \text{nor} \; \textbf{(B)} \; \text{nor} \; \textbf{(C)} \; \text{nor} \; \textbf{(D)} \; \text{is true}$


Solution

From the problem we can set the altitude equal to $a$, the shorter base equal to $a-d$, and the longer base equal to $a+d$. By the formula for the area of a trapezoid, we have $K=a^2$. However, since $a$ can equal any real number $(3, 2.7, \pi)$, none of the statements $A, B, C, D$ need to be true, so the answer is $\fbox{E}$.

See also

1967 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 8
Followed by
Problem 10
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 31 32 33 34 35 36 37 38 39 40
All AHSME Problems and Solutions

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