Out of 18 points in a plane no three are in the same straight line except five points which are collinear. The number of straight lines that can be formed joining them, is
A) 143
B) 144
C) 153
D) None of these
Correct Answer:
B
Solution :
The number of straight lines \[{{=}^{18}}{{C}_{2}}-{{(}^{5}}{{C}_{2}}-1)=144\]