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Question
Find the number of triangles formed by joining 12 points if four points are collinear
Solution
There are 12 points on the plane
When 4 of these points are collinear
∴ Number of triangles that can be obtained from these points = 12C3 – 4C3
= `220 - (4!)/(3! xx 1!)`
= `220 - (4 xx 3!)/(3!)`
= 220 – 4
= 216
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