There are 10 points on a plane.
(a) When no three of them are collinear. A line is obtained by joining 2 points.
∴ Number of lines passing through these points = 10C2
(b) When 4 of them are collinear. If no three points are collinear, we get a total of 10C2 = 45 lines by joining them. …..[From (a)]
Since 4 points are collinear, only one line passes through these points instead of 4C2 lines.
∴ C – 1 extra lines are included in 45 lines.
Number of lines passing through these points