how many lines can be drawn from 10 points out of which 4 points are collinear?

Straight line can be formed by joining 2 points

so number of ways in which we can select 2 points from 10 points is  = ¹⁰C₂

 but it also include that in which 4 points are in straight line . from those 4 points only one line can be formed .

so we have to subtract ⁴C₂ -1 from above result

Therefore, total number of lines = ¹⁰C₂   - ⁴C₂ + 1 = 45 - 6 + 1 = 40