Ratio

Geometry Level 3

In the given rectangle, find the ratio of area of shaded region to unshaded region in decimal.


The answer is 1.76.

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2 solutions

Harrison Wang
Aug 6, 2014

When placing the hypotenuses of each pair of right triangles together, we get two rectangles similar to each other. Thus the ratio of their areas is the square of the ratio of their diagonals: ( 8 6 ) 2 = 16 9 = 1. 7 \Big(\frac{8}{6}\Big)^2 = \frac{16}{9} = 1.\overline{7}

let (a) is the height of the two triangles (b) is the base of shaded triangle and (c) is the base of the unshaded triangle , 64=a^2+b^2 , 36=a^2+c^2 , b^2-c^2=28 , b+c=10 , b=10-c , (10-c)-c^2=28 , 100+c^2-20 c-c^2=28 , c=(100-28)/20
=3.6 , b=6.4 , area of shaded region A1=2
(0.5 a b) , area of unshaded region A2=a*c , A1/A2=b/c =1.777778

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