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NCERT Class XI Mathematics - Permutations and Combinations - Solutions

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Question : 24
Total: 41
How many chords can be drawn through 21 points on a circle?
Solution:  
A chord is formed by joining two points on a circle.
∴ Required number of chords =
21
‌
C2 =
21!
2!19!
 =
21×20
2
 = 210
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