Q. 15

# Mark the correct alternative in the following:There are 10 points in a plane and 4 of them are collinear. The number of straight lines joining any two of them isA. 45B. 40C. 39D. 38

Number of straight lines formed by joining the 10 points if we take 2 points at a time = 10C2

Number of straight lines formed by joining the 4 points if we take 2 points at a time = 4C2

But, 4 collinear points, when joined in pairs give only one line.

Required number of straight lines =

45 – 6 + 1

= 40

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