Question

Ten points are plotted on a plane. Find the number of straight lines obtained by joining these points if no three points are collinear.

Answer 1

To draw a line, two points are needed.
There are 10 points in a plane such that no three of them are collinear. 
Hence, the number of lines formed ¹⁰C₂

= `(10!)/((10 - 2)!2!)`

= `(10!)/(2!8!)`

= `(10 xx 9xx8!)/(2xx1xx8!)`

= 5 × 9
= 45
45 straight lines are obtained if no three points are collinear.