Teachers deny the question was too difficult (scroll to the bottom of the article for the solution).
But strong maths students made the mistake of overthinking the question, while weaker students froze up, believing there was not enough information to solve the question.
- The Age, 2nd Nov 2015
I bet I can solve the question without even drawing a diagram:
There are 360° in a circle.
The angle between 12 lines radiating from the centre to each corner is:
360°/ 12 = 30°
12 equaliateral triangles can be drawn.
The angle sum of a triangle is 180°
The other two angles in these equaliateral triangles is:
180° - 30° = 150° (two angles)
150° / 2 = 75° (two angles)
If a line is drawn which extends from a side. Two 75° angles rotate around a point.
Angles on one side of a straight line add up to 180°
180° - (75° * 2) = 30°
Two coins are side by side; so that angle must be reflected.
30° + 30° = 60°
The Answer is D.
I win a cookie. Time elapsed (22 seconds).