In mathematics, a combination is a selection of items from a set that has distinct members
Formula
[tex]^n_{^{}}C_r=\frac{n\text{ !}}{(n-r)!r!}[/tex]Where
n = 20
r =3
[tex]\begin{gathered} ^{20}C_3=\frac{20\text{ !}}{(20-3)!3!} \\ \\ \\ ^{20}C_3=\frac{20\text{ !}}{17!3!} \\ \\ \\ ^{20}C_3=\frac{20\text{ }\times19\times18\times17!}{17!3!} \\ ^{20}C_3=\frac{20\text{ }\times19\times18}{3!} \\ \\ ^{20}C_3=\frac{20\text{ }\times19\times18}{3\times2\times1} \\ ^{20}C_3=\frac{20\text{ }\times19\times18}{6} \\ \\ ^{20}C_3=20\text{ }\times19\times3 \\ \\ \\ ^{20}C_3=1140 \end{gathered}[/tex]The final answer
1140 unique groups of volunteers are possible
