Difficulty: Easy
Correct Answer: 360
Explanation:
Introduction / Context:
The number of triangles from a set of points is normally C(n, 3), but any collinear triple cannot form a triangle. We adjust by subtracting those degenerate triples.
Given Data / Assumptions:
Concept / Approach:
Valid triangles = total triples − collinear triples. Only the special set of 4 contributes collinear triples.
Step-by-Step Solution:
Total triples: C(14, 3) = 364.Collinear triples among the 4: C(4, 3) = 4.Triangles = 364 − 4 = 360.
Verification / Alternative check:
If no three were collinear, C(14, 3) would be correct. One collinear block reduces the count by exactly its C(4, 3) degenerate triples.
Why Other Options Are Wrong:
364 ignores collinearity; 368 and 365 exceed the possible total; 356 subtracts too many.
Common Pitfalls:
Subtracting C(4,2) instead of C(4,3) or double-counting.
Final Answer:
360
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