2013 AMC 8 Problem 23
Attempt Problem 23 of the 2013 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2013 AMC 8 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
23.
In , is a right angle. The sides of are the diameters of semicircles as shown. The area of the semicircle on equals and the arc of the semicircle on has length What is the radius of the semicircle on
Answer: B
Small hint:
Use the semicircle on to find .
Big hint:
The arc length on gives the radius, hence diameter .
Video solution:
Click to load, then click again to play
Written solution:
The semicircle on has area , so its full circle would have area . Its radius is therefore , and .
A semicircle of radius has arc length . Since the arc on has length , its radius is , so .
Using the Pythagorean theorem in right triangle , The radius of the semicircle on is .
Thus, B is the correct answer.
Problem 23 in other years
- 1985 AMC 8
- 1986 AMC 8
- 1987 AMC 8
- 1988 AMC 8
- 1989 AMC 8
- 1990 AMC 8
- 1991 AMC 8
- 1992 AMC 8
- 1993 AMC 8
- 1994 AMC 8
- 1995 AMC 8
- 1996 AMC 8
- 1997 AMC 8
- 1998 AMC 8
- 1999 AMC 8
- 2000 AMC 8
- 2001 AMC 8
- 2002 AMC 8
- 2003 AMC 8
- 2004 AMC 8
- 2005 AMC 8
- 2006 AMC 8
- 2007 AMC 8
- 2008 AMC 8
- 2009 AMC 8
- 2010 AMC 8
- 2011 AMC 8
- 2012 AMC 8
- 2014 AMC 8
- 2015 AMC 8
- 2016 AMC 8
- 2017 AMC 8
- 2018 AMC 8
- 2019 AMC 8
- 2020 AMC 8
- 2022 AMC 8
- 2023 AMC 8
- 2024 AMC 8
- 2025 AMC 8
- 2026 AMC 8