Selection of machines is persons choice and not arranged specifically, thus we will use Combination.
⇒ 20C5
⇒ 20!/5!(20-5)!
⇒ 15504
Use combination
total ways
[tex]\\ \rm\dashrightarrow ^nC_r=\dfrac{n!}{r!(n-r)!}[/tex]
[tex]\\ \rm\dashrightarrow ^{20}C_5[/tex]
[tex]\\ \rm\dashrightarrow \dfrac{20!}{5!15!}[/tex]
[tex]\\ \rm\dashrightarrow \dfrac{20(19)(18)(17)(16)(15!)}{5(4)(3)(2)(15!}[/tex]
[tex]\\ \rm\dashrightarrow 15504[/tex]
