Mark the correct alternative in the following:
There are 10 points in a plane and 4 of them are collinear. The number of straight lines joining any two of them is
Number of straight lines formed by joining the 10 points if we take 2 points at a time = 10C2
Number of straight lines formed by joining the 4 points if we take 2 points at a time = 4C2
But, 4 collinear points, when joined in pairs give only one line.
Required number of straight lines =
45 – 6 + 1
= 40