2013 AMC 8 Problem 24

Attempt Problem 24 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).

24.

Squares ABCD,ABCD, EFGH,EFGH, and GHIJGHIJ are equal in area. Points CC and DD are the midpoints of sides IHIH and HE,HE, respectively. What is the ratio of the area of the shaded pentagon AJICBAJICB to the sum of the areas of the three squares?
14\dfrac{1}{4}
724\dfrac{7}{24}
13\dfrac{1}{3}
38\dfrac{3}{8}
512\dfrac{5}{12}
Answer: C
Concepts:area decompositiontriangle area
Small hint:
Let each square have side length 11.
Big hint:
Subtract the unshaded rectangle and triangle from the total area 33.
Video solution:
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Written solution:
Let each square have side length 11, so the total area of the three squares is 33. It is easier to subtract the unshaded region to the left of diagonal AJAJ from this total.
Using the solution diagram, rectangle EDKFEDKF has area 1⋅12=121\cdot\dfrac12=\dfrac12, and triangle AKJAKJ has area 12⋅32⋅2=32.\dfrac12\cdot\dfrac32\cdot2=\dfrac32. Thus the unshaded area is 12+32=2\dfrac12+\dfrac32=2, so the shaded pentagon has area 3−2=13-2=1.
The requested ratio is 13\dfrac{1}{3}.
Thus, C is the correct answer.
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