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If 20cr + 1 = 20cr − 1 , Then R is Equal to (A) 10 (B) 11 (C) 19 (D) 12 - Mathematics

MCQ

If 20Cr + 1 = 20Cr − 1 , then r is equal to

Options

  • 10

  • 11

  •  19

  • 12

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Solution

10

\[r + 1 + r - 1 = 20\] [∵\[{}^n C_x =^n C_y \Rightarrow n = x + y or x = y\]]
\[\Rightarrow 2r = 20\]
\[ \Rightarrow r = 10\]
  Is there an error in this question or solution?
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APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 17 Combinations
Q 4 | Page 25
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