There are 10 points in a plane and 4 of them are collinear. The number of straight lines joining any two of them is

Options

A. 45
B. 40
C. 39
D. 38

Answer

B

Explanation

A straight line can be drawn joining two points, so there will be ` ""^(10)C_(2)` straight lines joining 10 points. but 4 of them are collinear, so we shall get only one line joining any two of these 4 points. Hence the total number of lines = ` ""^(10)C_(2) - ""^(4)C_(2) + 1 = 40`
Ans.[2]