Permutations and Combinations 2 Question 15

15. Let n2 be an integer. Take n distinct points on a circle and join each pair of points by a line segment. Colour the line segment joining every pair of adjacent points by blue and the rest by red. If the number of red and blue line segments are equal, then the value of n is

(2014 Adv)

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Answer:

Correct Answer: 15. (5)

Solution:

  1. PLAN Number of line segment joining pair of adjacent point =n Number of line segment obtained joining n points on a circle =nC2

 Number of red line segments =nC2n

Number of blue line segments =n

nC2n=nn(n1)2=2nn=5



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