# there are 10 points ina aplane of which 3 are collinear.how many straight lines wecan drawn ?

Vaishal Shah
50 Points
11 years ago
10c2-3c2+1 where c is combination =45-3+1 =43
Aman Bansal
592 Points
11 years ago

Dear Mangati,

Case 1: We choose two of the four collinear points. Here, only one line is determined because we cannot count 4C2 lines (they are all the same).

Case 2: We choose two of the six other non-collinear points. Here, it is simply choosing any two points out of 6, 6C2 = 15.

Case 3: We choose one of the four collinear points, and one of the six remaining points. There are 4*6 = 24 lines determined, no two of which are collinear.

The number of lines is 1+15+24 = 40.

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Aman Bansal