There are 10 points in a plane, no three of which are in the same straight line, except 4 points, which are collinear. Find the number of lines obtained from the pairs of these points,A. 40B. 39C. 45D. none of these

There are 10 points in a plane, no three of which are in the same stra

1.	There are 10 points in a plane, no three of which are in the same straight line, except 4 points, which are collinear. Find the number of lines obtained from the pairs of these points,A. 40B. 39C. 45D. none of these
Answer» Number of stright lines formed joining the 10 points, taking 2 at a time `""^(10)C_(2)=(10!)/(2!8!)=45`. Number of straight lines formed by joining the four points, taking 2 at a time `""^(4)C_(2)=(4!)/(2!2!)=6` But, 4 collinear points, when joined pairwise give only one line. `:.` Required number of straight lines =45-6+1=40.

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There are 10 points in a plane, no three of which are in the same straight line, except 4 points, which are collinear. Find the number of lines obtained from the pairs of these points,A. 40B. 39C. 45D. none of these

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