Difference between revisions of "1959 AHSME Problems/Problem 22"
m (improved clarity) |
|||
(4 intermediate revisions by the same user not shown) | |||
Line 2: | Line 2: | ||
The line joining the midpoints of the diagonals of a trapezoid has length <math>3</math>. If the longer base is <math>97,</math> then the shorter base is: <math>\textbf{(A)}\ 94 \qquad\textbf{(B)}\ 92\qquad\textbf{(C)}\ 91\qquad\textbf{(D)}\ 90\qquad\textbf{(E)}\ 89</math> | The line joining the midpoints of the diagonals of a trapezoid has length <math>3</math>. If the longer base is <math>97,</math> then the shorter base is: <math>\textbf{(A)}\ 94 \qquad\textbf{(B)}\ 92\qquad\textbf{(C)}\ 91\qquad\textbf{(D)}\ 90\qquad\textbf{(E)}\ 89</math> | ||
− | == Solution == | + | == Solution 1 == |
− | |||
− | |||
− | + | <asy> | |
− | + | import geometry; | |
− | Thus, 91. | + | point B = (0,0); |
+ | point A = (3,5); | ||
+ | point D = (13,5); | ||
+ | point C = (15,0); | ||
+ | point M,N; | ||
+ | |||
+ | // Trapezoid | ||
+ | draw(A--B--C--D--A); | ||
+ | dot(A); | ||
+ | label("A",A,NW); | ||
+ | dot(B); | ||
+ | label("B",B,SW); | ||
+ | dot(C); | ||
+ | label("C",C,SE); | ||
+ | dot(D); | ||
+ | label("D",D,NE); | ||
+ | |||
+ | // Diagonals and their midpoints | ||
+ | draw(A--C); | ||
+ | draw(B--D); | ||
+ | |||
+ | M = midpoint(A--C); | ||
+ | dot(M); | ||
+ | label("M",M,ENE); | ||
+ | |||
+ | N = midpoint(B--D); | ||
+ | dot(N); | ||
+ | label("N",N,WNW); | ||
+ | draw(M--N); | ||
+ | |||
+ | // Length Labels | ||
+ | label("$x$",midpoint(A--D),(0,1)); | ||
+ | label("$97$",midpoint(B--C),S); | ||
+ | label("$3$",midpoint(M--N),S); | ||
+ | |||
+ | </asy> | ||
+ | |||
+ | Let <math>x</math> be the length of the shorter base. Then: | ||
+ | |||
+ | <math>3 = \frac{97-x}{2}</math> | ||
+ | |||
+ | <math>6 = 97-x</math> | ||
+ | |||
+ | <math>x = 91</math> | ||
+ | |||
+ | Thus, our answer is <math>\boxed{\textbf{(C) }91}</math>. | ||
+ | |||
+ | == Solution 2 == | ||
+ | Let the trapezoid be <math>ABCD</math> with <math>\overline{AD} \parallel \overline{BC}</math>, with <math>M</math> as the midpoint of <math>\overline{AC}</math>, and <math>N</math> as the midpoint of <math>\overline{BD}</math>, as in the diagram. As in the first solution, let the shorter base of the trapezoid (<math>\overline{AD}</math>) have length <math>x</math>. Because <math>\overline{AD} \parallel \overline{BC}</math>, we can imagine shifting <math>\overline{AC}</math> along <math>\overleftrightarrow{BC}</math> by distance <math>x</math> such that <math>A</math> is at <math>D</math>, at which point we get the following triangle: | ||
+ | |||
+ | <asy> | ||
+ | |||
+ | import geometry; | ||
+ | |||
+ | size(10cm); | ||
+ | |||
+ | point B = (0,0); | ||
+ | point C = (25,0); | ||
+ | point A = (13,5); | ||
+ | point M,N; | ||
+ | |||
+ | // Triangle ABC | ||
+ | draw(A--B--C--A); | ||
+ | dot(A); | ||
+ | label("A",A,(0,1)); | ||
+ | dot(B); | ||
+ | label("B",B,SW); | ||
+ | dot(C); | ||
+ | label("C",C,SE); | ||
+ | |||
+ | |||
+ | // Midpoint connector | ||
+ | M = midpoint(A--C); | ||
+ | dot(M); | ||
+ | label("M",M,NE); | ||
+ | N = midpoint(B--A); | ||
+ | dot(N); | ||
+ | label("N",N,NW); | ||
+ | draw(M--N); | ||
+ | |||
+ | // Length Labels | ||
+ | label("$97+x$",midpoint(B--C),S); | ||
+ | label("$3+x$",midpoint(M--N),S); | ||
+ | |||
+ | </asy> | ||
+ | |||
+ | Because <math>\overline{MN}</math> is a [[Midpoint#Midsegments|midpoint connector]] of <math>\triangle ABC</math>, <math>MN=\frac{1}{2}BC</math>, and so we have the equation <math>3+x=\frac{97+x}{2}</math>. Solving for <math>x</math> yields <math>x=\boxed{\textbf{(C) }91}</math>. | ||
+ | |||
+ | ==See also== | ||
+ | {{AHSME 50p box|year=1959|num-b=21|num-a=23}} | ||
+ | {{MAA Notice}} | ||
+ | [[Category:Introductory Geometry Problems]] |
Latest revision as of 12:20, 21 July 2024
Contents
Problem
The line joining the midpoints of the diagonals of a trapezoid has length . If the longer base is then the shorter base is:
Solution 1
Let be the length of the shorter base. Then:
Thus, our answer is .
Solution 2
Let the trapezoid be with , with as the midpoint of , and as the midpoint of , as in the diagram. As in the first solution, let the shorter base of the trapezoid () have length . Because , we can imagine shifting along by distance such that is at , at which point we get the following triangle:
Because is a midpoint connector of , , and so we have the equation . Solving for yields .
See also
1959 AHSC (Problems • Answer Key • Resources) | ||
Preceded by Problem 21 |
Followed by Problem 23 | |
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 • 41 • 42 • 43 • 44 • 45 • 46 • 47 • 48 • 49 • 50 | ||
All AHSME Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.