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If 15c3r = 15cr + 3, Find R. - Mathematics

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If 15C3r = 15Cr + 3, find r.

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Solution

Given:
 15C3r = 15Cr + 3

\[15 = 3r + r + 3 .\]  [∵\[{}^n C_x = {}^n C_y \Rightarrow x = y\]] or, \[n = x + y\]
\[\Rightarrow 15 = 4r + 3\]
\[ \Rightarrow 4r = 12\]
\[ \Rightarrow r = 3\]
Concept: Combination
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APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 17 Combinations
Exercise 17.1 | Q 7 | Page 8

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