Question Number 196347 by bbbbbbbb last updated on 23/Aug/23
$$\left(\mathrm{1}\overset{\left(\mathrm{2}\overset{\mathrm{21}} {\mathrm{0}}\right)} {\mathrm{9}}\right)\:\boldsymbol{\mathrm{factorial}}\:\boldsymbol{\mathrm{plz}}\:\boldsymbol{\mathrm{hepl}}\:\boldsymbol{\mathrm{me}}\:\boldsymbol{\mathrm{so}}\:\boldsymbol{\mathrm{soon}} \\ $$
Commented by mr W last updated on 23/Aug/23
$${so}\:{soon}\:{as}\:{the}\:{light}? \\ $$$${in}\:{each}\:{of}\:{your}\:{questions}\:{you}\:{request} \\ $$$${people}\:{to}\:{help}\:{you}\:{soon},\:{why}\:{should} \\ $$$${they}? \\ $$$${if}\:{you}\:{have}\:{exam}\:{in}\:\mathrm{5}\:{minutes},\:{you} \\ $$$${can}'{t}\:{expect}\:{that}\:{people}\:{give}\:{you}\:{the} \\ $$$${answer}\:{in}\:\mathrm{2}\:{minutes}.\:{better}\:{you}\:{put} \\ $$$${your}\:{question}\:\mathrm{2}\:{days}\:{earlier}. \\ $$
Commented by bbbbbbbb last updated on 23/Aug/23
$$ \\ $$$$\mathrm{okay}\:\mathrm{dear}\:\mathrm{iwill}\:\mathrm{try}\:\mathrm{dear} \\ $$
Commented by MATHEMATICSAM last updated on 23/Aug/23
$$\mathrm{yes}\:\mathrm{right} \\ $$
Answered by mr W last updated on 23/Aug/23
$$\begin{pmatrix}{\mathrm{21}}\\{\mathrm{20}}\end{pmatrix}=\frac{\mathrm{21}!}{\mathrm{20}!\mathrm{1}!}=\mathrm{21} \\ $$$$\begin{pmatrix}{\begin{pmatrix}{\mathrm{21}}\\{\mathrm{20}}\end{pmatrix}}\\{\mathrm{19}}\end{pmatrix}=\begin{pmatrix}{\mathrm{21}}\\{\mathrm{19}}\end{pmatrix}=\frac{\mathrm{21}!}{\mathrm{19}!×\mathrm{2}!}=\frac{\mathrm{21}×\mathrm{20}}{\mathrm{2}}=\mathrm{210} \\ $$