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6.Permutation and Combination
normal
$_nC_{r+1} + _nC_{r-1} + 2_n C_r = ….$
A
$_{n+1}C_{r+1}$
B
${n+2}C_r$
C
$_{n+2} C_{r+1}$
D
$_{n+1} Cr$
Solution
$_nC_{r+1} + _nC_{r-1} + 2_nC_r+ = [ _nC_{r+1} + _nC_r ]+ [ _nC_r + _nC_{r-1} $
=$ _{n+1}C_{r+1} +{ n+1}C_r = _{n+2}C_{r+1}$
Standard 11
Mathematics