JEE Main 2024 Mathematics question
The number of triangles whose vertices are at the vertices of a regular octagon but none of whose sides is a side of the octagon is
Answer: (C)
Solution
Total C(8,3) = 56. Triangles with two octagon sides: 8; with exactly one side: 8 × 4 = 32. So 56 − 8 − 32 = 16.