\({20 \choose 4}\) sodas (order does not matter and repeats are not allowed).
\(P(20, 4) = 20\cdot 19\cdot 18 \cdot 17\) sodas (order matters and repeats are not allowed).
\({23 \choose 4}\) sodas (order does not matter and repeats are allowed; 4 stars and 19 bars).
\(20^4\) sodas (order matters and repeats are allowed; 20 choices 4 times).