In the triangles that can be made by connecting three vertices of regular decagon, find the number of triangles whose sides are not shared with the regular decagon.
Answer
50 pieces
Solution
The number of triangles with which 2 sides are shared is 10 pieces.
Answer
50 pieces
Solution
The number of triangles with which 2 sides are shared is 10 pieces.
The number of triangles with which 1 side is shared is 6 × 10 = 60 pieces.
As total number of triangles altogether is (10 × 9 × 8) / (3 × 2 × 1) = 120, number of triangles to be found is 120 - 70 = 50 pieces.
