2015 AMC 12B Problem 24
Attempt Problem 24 of the 2015 AMC 12B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2015 AMC 12B solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
24.
Four circles, no two of which are congruent, have centers at and and points and lie on all four circles. The radius of circle is times the radius of circle and the radius of circle is times the radius of circle Furthermore, and Let be the midpoint of What is
Answer: D
Solution:
Since every center is equidistant from and all four centers and lie on the perpendicular bisector of with First consider two centers whose radii are in the ratio and whose distance apart is If lies between them, let and of circle 's radius. Then and Subtracting gives so and Here so the two center distances from are and and the radii are and
If instead the two centers lie on the same side of their distances are and The analogous equations give hence and the distances are and In this case the radii are and Using the same placement for both pairs and would give two congruent circles of each radius, contrary to the hypothesis. Thus one pair uses each placement. Their distance sums are and so the requested total is
Thus, the correct answer is D.
Problem 24 in Other Years
1999 AMC 12 · 2000 AMC 12 · 2001 AMC 12 · 2002 AMC 12A · 2002 AMC 12B · 2003 AMC 12A · 2003 AMC 12B · 2004 AMC 12A · 2004 AMC 12B · 2005 AMC 12A · 2005 AMC 12B · 2006 AMC 12A · 2006 AMC 12B · 2007 AMC 12A · 2007 AMC 12B · 2008 AMC 12A · 2008 AMC 12B · 2009 AMC 12A · 2009 AMC 12B · 2010 AMC 12A · 2010 AMC 12B · 2011 AMC 12A · 2011 AMC 12B · 2012 AMC 12A · 2012 AMC 12B · 2013 AMC 12A · 2013 AMC 12B · 2014 AMC 12A · 2014 AMC 12B · 2015 AMC 12A · 2016 AMC 12A · 2016 AMC 12B · 2017 AMC 12A · 2017 AMC 12B · 2018 AMC 12A · 2018 AMC 12B · 2019 AMC 12A · 2019 AMC 12B · 2020 AMC 12A · 2020 AMC 12B · 2021 AMC 12A Spring · 2021 AMC 12B Spring · 2021 AMC 12A Fall · 2021 AMC 12B Fall · 2022 AMC 12A · 2022 AMC 12B · 2023 AMC 12A · 2023 AMC 12B · 2024 AMC 12A · 2024 AMC 12B · 2025 AMC 12A · 2025 AMC 12B