1999 AIME Problem 15
Below is the professionally curated solution for Problem 15 of the 1999 AIME, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1999 AIME solutions, or check the answer key.
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Difficulty rating: 2990
15.
Consider the paper triangle whose vertices are and The vertices of its midpoint triangle are the midpoints of its sides. A triangular pyramid is formed by folding the triangle along the sides of its midpoint triangle. What is the volume of this pyramid?
Solution:
The midpoints are and Folding the three corner triangles up along the sides of the midpoint triangle brings the corners together at one apex (each pair of glued half-sides has equal length). The apex keeps its folded distances: (half of the side of length that bisects), (half of ), and (half of ).
Keep the midpoint triangle in the plane and let Subtracting from gives so subtracting from gives so Then so the apex is at height
The base is the midpoint triangle, with area one quarter of the original triangle's i.e. The volume is
Problem 15 in Other Years
1997 AIME · 1998 AIME · 2000 AIME I · 2000 AIME II · 2001 AIME I · 2001 AIME II · 2002 AIME I · 2002 AIME II · 2003 AIME I · 2003 AIME II · 2004 AIME I · 2004 AIME II · 2005 AIME I · 2005 AIME II · 2006 AIME I · 2006 AIME II · 2007 AIME I · 2007 AIME II · 2008 AIME I · 2008 AIME II · 2009 AIME I · 2009 AIME II · 2010 AIME I · 2010 AIME II · 2011 AIME I · 2011 AIME II · 2012 AIME I · 2012 AIME II · 2013 AIME I · 2013 AIME II · 2014 AIME I · 2014 AIME II · 2015 AIME I · 2015 AIME II · 2016 AIME I · 2016 AIME II · 2017 AIME I · 2017 AIME II · 2018 AIME I · 2018 AIME II · 2019 AIME I · 2019 AIME II · 2020 AIME I · 2020 AIME II · 2021 AIME I · 2021 AIME II · 2022 AIME I · 2022 AIME II · 2023 AIME I · 2023 AIME II · 2024 AIME I · 2024 AIME II · 2025 AIME I · 2025 AIME II · 2026 AIME I · 2026 AIME II