Mark the correct alternative in the following:
There are 12 points in a plane. The number of the straight lines joining any two of them when 3 of them are collinear, is
Number of straight lines joining 12 points if we take 2 points at a time = 12C2
= 66
Number of straight lines joining 3 points if we take 2 points at a time = 3C2
= 3
But, 3 collinear points, when joined in pairs gives only one line.
Required number of straight lines =
66 – 3 + 1
= 64