# 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

• 10

• 11

•  19

• 12

#### Solution

10

$r + 1 + r - 1 = 20$ [∵${}^n C_x =^n C_y \Rightarrow n = x + y or x = y$]
$\Rightarrow 2r = 20$
$\Rightarrow r = 10$
Concept: Combination
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#### APPEARS IN

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