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MathNet 2009-part-03 — 175 problems (EN–VI) Question 159

Math Olympiad Vault · MathNet 2009-part-03 — 175 problems (EN–VI)

Question 159

$n$ lines are drawn in the plane, and all the intersection points of these lines are marked. It appears that one of the $n$ lines contains exactly 1 marked point, one of the $n$ lines contains exactly 3 marked points, and one of the $n$ lines contains exactly 5 marked points. Find all the possible values of $n$. (I. Bogdanov)