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, isA. 62B. 63C. 64D. 65

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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