Q. 12

Mark the correct alternative in the following:

There are 12 points in a plane. The number of the straight lines joining any two of them when 3 of them are collinear, is

A. 62

B. 63

C. 64

D. 65

Answer :

Number of straight lines joining 12 points if we take 2 points at a time = 12C2



= 66


Number of straight lines joining 3 points if we take 2 points at a time = 3C2


= 3


But, 3 collinear points, when joined in pairs gives only one line.


Required number of straight lines =


66 – 3 + 1


= 64

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