Problem 14 · 2010 Math Kangaroo
Medium
Geometry & Measurement
symmetry
How big is the angle indicated with a question mark?
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Answer: D — 40°
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Hint 1 of 2
The 330 degree mark is a reflex angle, so the actual angle at that corner is 360 - 330.
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Hint 2 of 2
Use the right-angle mark and the 20 degrees together with triangle angle sums to chase the unknown.
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Approach: angle chasing with the given marks
- The reflex 330 degrees means that corner's angle is 360 - 330 = 30 degrees.
- Combining this with the marked right angle and the 20 degrees through the triangles, the unknown angle works out to 40 degrees.
Mark:
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