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Problem 278 Difficulty 1.5 Multiple choice CEMC Gauss (Grade 7) · Canada · 2015
In the rectangle shown, the area of the shaded region is
Pick one
A 60 60 60 2 ^2 2 B 20 20 20 2 ^2 2 C 30 30 30 2 ^2 2 D 40 40 40 2 ^2 2 E 50 50 50 2 ^2 2
Show the answer
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Official solution The rectangle has area 5 × 12 = 60 5\times12=60 5 × 12 = 60 2 ^2 2
Each of the two congruent unshaded triangles has area 1 2 × 2 × 5 = 5 \frac12\times2\times5=5 2 1 × 2 × 5 = 5 2 ^2 2 60 − 5 − 5 = 50 60-5-5=50 60 − 5 − 5 = 50 2 ^2 2
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Source: CEMC, University of Waterloo ,
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