Difference between revisions of "2015 AMC 10B Problems/Problem 17"
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Revision as of 17:49, 18 May 2015
Problem
The centers of the faces of the right rectangular prism shown below are joined to create an octahedron, What is the volume of the octahedron?
![[asy] import three; size(2inch); currentprojection=orthographic(4,2,2); draw((0,0,0)--(0,0,3),dashed); draw((0,0,0)--(0,4,0),dashed); draw((0,0,0)--(5,0,0),dashed); draw((5,4,3)--(5,0,3)--(5,0,0)--(5,4,0)--(0,4,0)--(0,4,3)--(0,0,3)--(5,0,3)); draw((0,4,3)--(5,4,3)--(5,4,0)); label("3",(5,0,3)--(5,0,0),W); label("4",(5,0,0)--(5,4,0),S); label("5",(5,4,0)--(0,4,0),SE); [/asy]](http://latex.artofproblemsolving.com/0/f/e/0fecfb360827e29c3e9ad69126c0215a16cfd2ab.png)
Solution
The octahedron is just two congruent pyramids glued together. The base of one of the pyramids is a rhombus with diagonals 
and 
, for an area of 
. The height of one of the pyramids is then 
, so the volume is 
. Thus, the octahedron has volume 
See Also
| 2015 AMC 10B (Problems • Answer Key • Resources) | ||
| Preceded by Problem 16 |
Followed by Problem 18 | |
| 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 10 Problems and Solutions | ||
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