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Question
Find the number of triangles formed by joining 12 points if no three points are collinear
Solution
A triangle can be formed by selecting 3 non-collinear points.
We can choose 3 points from 12 points in
12C3 = `(12!)/(3!9!)`
= `(12 xx 11 xx 10 xx 9!)/(3 xx 2 xx 1 xx 9!)`
= 220 ways
∴ number of triangles = 220.
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