How many straight lines can be drawn through 10 points of which 4 are collinear?
Solution
Total lines C(10,2) = 45. Lines through 4 collinear points (all same line): C(4,2) = 6 lines counted in the 45 that are actually just 1 line each. So we subtract the extra count: 45 - (6-1) = 45 - 5 = 40. Actually: 45 - 6 (these 6 counted once but represent 1 line) + 1 = 40. So answer = 40.
About this question
Subject: Mathematics · Chapter: Permutations and Combinations · Topic: Applications
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