6.Permutation and Combination
normal

$^{20}C_1 + 3 ^{20}C_2 + 3 ^{20}C_3 + ^{20}C_4$ is equal to-

A

$^{20}C_4$

B

$2. ^{21}C_4$

C

$2. ^{22}C_4$

D

$^{23}C_4$

Solution

$({\,^{20}}{{\rm{C}}_1} + 2{\,^{20}}{{\rm{C}}_2} + {\,^{20}}{{\rm{C}}_3}{\rm{)}} + {{\rm{(}}^{20}}{{\rm{C}}_2} + 2{\,^{20}}{{\rm{C}}_3} + {\,^{20}}{{\rm{C}}_4}{\rm{)}}$

$ \Rightarrow {\,^{22}}{C_3} + {\,^{22}}{C_4} = {\,^{23}}{C_4}$

Standard 11
Mathematics

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