Maths Olympiad Prep

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Geometry Difficulty 3.3 AMC 10/12 Find the answer

The area of polygon ABCDEFABCDEF, in square units, is

Pick one

Solution

Obviously, there are no formulas to find the area of such a messed up shape, but we do recognize some shapes we do know how to find the area of.
If we continue segment FE\overline{FE} until it reaches the right side at GG, we create two rectangles - one on the top and one on the bottom.
We know how to find the area of a rectangle, and we're given the sides! We can easily find that the area of ABGFABGF is 6×5=306\times5 = 30. For the rectangle on the bottom, we do know the length of one of its sides, but we don't know the other.
Note that GC+GB=9GC+GB=9, and GB=AF=5GB=AF=5, so we must have GC+5=9GC=4GC+5=9\Rightarrow GC=4
The area of the bottom rectangle is then (DC)(GC)=4×4=16(DC)(GC)=4\times 4=16
Finally, we just add the areas of the rectangles together to get 16+30=4616 + 30 = 46.
C\boxed{\text{C}}

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.