We check the following points
1. The order does not matters
2. No repetition
3. we cannot choose all the available choices. we need to select only 4
If order does not matters then we use combination
Formula is nCr = [tex] \frac{n!}{r!(n-r)!} [/tex]
We choose 4 from 9
So 9C4 = [tex] \frac{9!}{4!(9-4)!} [/tex]
= [tex] \frac{9!}{4!(5)!} [/tex] = 126 ways