Q. 45.0( 2 Votes )

# Out of 18 points in a plane, no three are in the same line except five points which are collinear. Find the number of lines that can be formed joining the point.

[Hint: Number of straight lines =^{18}C_{2} – ^{5}C_{2} + 1]

Answer :

Formula:- (i)^{n}C_{r}

Given:-

Number of points =18

Number of Collinear points =5

Number of lines form by 18 points =^{18}C_{2}

For 5 points are collinear=^{5}C_{2}

the number of lines that can be formed joining the point.

=^{18}C_{2}-^{5}C_{2}+1

=153-10+1

=144

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