Difference between revisions of "2022 AMC 8 Problems/Problem 24"
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label("$6$",midpoint(H--F),1.5*S,red); | label("$6$",midpoint(H--F),1.5*S,red); | ||
label("$8$",midpoint(H--J),1.5*W,red); | label("$8$",midpoint(H--J),1.5*W,red); | ||
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| + | /* -._-. (edited by Lvluo .-_.- :) */ | ||
</asy> | </asy> | ||
Then the volume of this triangular prism is <math>8 \times \frac {6 \times 8}{2} = \boxed{\textbf{(C) }192}</math>. | Then the volume of this triangular prism is <math>8 \times \frac {6 \times 8}{2} = \boxed{\textbf{(C) }192}</math>. | ||
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~MRENTHUSIASM | ~MRENTHUSIASM | ||
Revision as of 16:13, 7 June 2022
Problem
The figure below shows a polygon 
, consisting of rectangles and right triangles. When cut out and folded on the dotted lines, the polygon forms a triangular prism. Suppose that 
and 
. What is the volume of the prism?
![[asy] usepackage("mathptmx"); size(275); defaultpen(linewidth(0.8)); real r = 2, s = 2.5, theta = 14; pair G = (0,0), F = (r,0), C = (r,s), B = (0,s), M = (C+F)/2, I = M + s/2 * dir(-theta); pair N = (B+G)/2, J = N + s/2 * dir(180+theta); pair E = F + r * dir(- 45 - theta/2), D = I+E-F; pair H = J + r * dir(135 + theta/2), A = B+H-J; draw(A--B--C--I--D--E--F--G--J--H--cycle^^rightanglemark(F,I,C)^^rightanglemark(G,J,B)); draw(J--B--G^^C--F--I,linetype ("4 4")); dot("$A$",A,N); dot("$B$",B,1.2*N); dot("$C$",C,N); dot("$D$",D,dir(0)); dot("$E$",E,S); dot("$F$",F,1.5*dir(-100)); dot("$G$",G,S); dot("$H$",H,W); dot("$I$",I,NE); dot("$J$",J,1.5*S); [/asy]](http://latex.artofproblemsolving.com/8/c/0/8c0183579e57a39614f2c3be1824f286b6bf4b86.png)
Solution
While imagining the folding, 
goes on 
goes on 
and 
goes on 
So, 
and 
Also, 
becomes an edge parallel to 
so that means 
Since 
then 
So, the area of 
is 
If we let be the base, then the height is 
So, the volume is 
Solution by aops-g5-gethsemanea2
Solution 2
After folding polygon on the dotted lines, we obtain the following triangular prism:
![[asy] /* Made by MRENTHUSIASM -._-.(edited by Lvluo) :D .-_.-*/ usepackage("mathptmx"); size(200); defaultpen(linewidth(0.8)); import graph3; import solids; currentprojection=orthographic((0.3,-0.3,0.3)); triple J, G, B, A, H, F; J = (0,0,0); G = (6,0,0); B = (0,8,0); A = (0,8,8); H = (0,0,8); F = (6,0,8); draw(surface(B--J--G--cycle),yellow); draw(surface(H--A--F--cycle),yellow); draw(B--J,dashed); draw(G--J--H--A--B^^A--F--H^^F--G^^B--G); draw((0.5,0,0)--(0.5,0.5,0)--(0,0.5,0)^^(0.5,0,8)--(0.5,0.5,8)--(0,0.5,8)); dot("$A=C$",A,1.5*E); dot("$B$",B,1.5*E); dot("$D=J$",J,1.5*W); dot("$F$",F,1.5*E); dot("$H=I$",H,1.5*W); dot("$E=G$",G,1.5*E); label("$8$",midpoint(A--H),1.5*NW,red); label("$6$",midpoint(H--F),1.5*S,red); label("$8$",midpoint(H--J),1.5*W,red); /* -._-. (edited by Lvluo .-_.- :) */ [/asy]](http://latex.artofproblemsolving.com/2/1/2/21235291bac98beb856efe17f49ebe0b3da44e97.png)
Then the volume of this triangular prism is 
.
~MRENTHUSIASM
Video Solution
https://www.youtube.com/watch?v=2uoBPp4Kxck
~Mathematical Dexterity
Video Solution
https://youtu.be/Ij9pAy6tQSg?t=2432
~Interstigation
See Also
| 2022 AMC 8 (Problems • Answer Key • Resources) | ||
| Preceded by Problem 23 |
Followed by Problem 25 | |
| 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 AJHSME/AMC 8 Problems and Solutions | ||
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
