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There are 25 points on a plane of which 7 are collinear . How many quadrilaterals can be formed from these points ?
A quadrilateral is formed from 4 points where at most 2 can be colinear.
So, from total subtract unwanted possibilities
(Total ways) - (ways to pick 4 colinear points) - (ways to pick 3 colinear points)
ans = 25C4 - 7C4 - 7C3 . 18C1