JEE AdvancedMathematicsPermutations and CombinationsNumerical+3 / −1
Let 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
Numerical answer
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Correct answer: 5
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Count the total number of line segments formed by joining every pair of points
With distinct points on a circle, joining every pair gives line segments in total.
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Count the blue line segments
Adjacent points on a circle form the sides of the polygon determined by the points.
Hence, the number of blue line segments is exactly
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Count the red line segments
All remaining segments are red, so
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Use the condition that red and blue segments are equal
Given:
So,
Substitute :
Multiply by :
Since , divide by :
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Conclusion
The required integer value is
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