Question
How many different straight lines can be formed by joining 14 different points of which 6 are collinear and rest are non-collinear?
Answer: Option D
:
D
No. of lines formed by joining 14 points =14C2
No. of lines formed by joining 6 points =6C2
Out of the 14 points, when you join the 6 collinear points, you don’t get6C2lines, but you get only one line.
So, no. of lines=14C2−6C2+1=91−15+1=77.
2nd method:- By selection, 8C2+8C1×6C1+1=77.
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:
D
No. of lines formed by joining 14 points =14C2
No. of lines formed by joining 6 points =6C2
Out of the 14 points, when you join the 6 collinear points, you don’t get6C2lines, but you get only one line.
So, no. of lines=14C2−6C2+1=91−15+1=77.
2nd method:- By selection, 8C2+8C1×6C1+1=77.
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