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6.Permutation and Combination
medium

જો $\left( {_{\,2}^{10}} \right) + \left( {_{\,3}^{10}} \right) + \left( {_{\,4}^{11}} \right) + \left( {_{\,5}^{12}} \right) + \left( {_{\,6}^{13}} \right) = \left( {_{\,r}^{14}} \right)\,\,$  હોય, $r\, = \,\,.........$

A

$4$

B

$5$

C

$6$

D

$7$

Solution

$\left( {\begin{array}{*{20}{c}}
  n \\ 
  {r – 1} 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  n \\ 
  r 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {n + 1} \\ 
  r 
\end{array}} \right)$  મળે .

અહી $ \left( {\begin{array}{*{20}{c}}
  {10} \\ 
  2 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {10} \\ 
  3 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {11} \\ 
  4 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {12} \\ 
  5 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {13} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)$

$\left( {\begin{array}{*{20}{c}}
  {11} \\ 
  3 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {11} \\ 
  4 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {12} \\ 
  5 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {13} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)\,\,\,\,$

$\left( {\begin{array}{*{20}{c}}
  {12} \\ 
  4 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {12} \\ 
  5 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {13} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)\,\,$

$\left( {\begin{array}{*{20}{c}}
  {12} \\ 
  4 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {12} \\ 
  5 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {13} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)$

$\left( {\begin{array}{*{20}{c}}
  {13} \\ 
  5 
\end{array}} \right) + \left( {\begin{array}{*{20}{c}}
  {13} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)\,\,\,$

$\left( {\begin{array}{*{20}{c}}
  {14} \\ 
  6 
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
  {14} \\ 
  r 
\end{array}} \right)\,\,\,$

$r = 6$

Standard 11
Mathematics

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