Chapter 11 - Counting Methods and Probability Theory - 11.3 Combinations - Exercise Set 11.3 - Page 708: 45

$1140$ ways

The order in which the members are chosen is not important Combinations, ${}_{n}C_{r}=\displaystyle \frac{n!}{(n-r)!r!}$ ${}_{20}C_{3}=\displaystyle \frac{20!}{(20-3)!3!}=\frac{20\times 19\times 18}{1\times 2\times 3}$ $=20\times 19\times 3=1140$