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1. \({20 \choose 4}\) sodas (order does not matter and repeats are not allowed).

2. \(P(20, 4) = 20\cdot 19\cdot 18 \cdot 17\) sodas (order matters and repeats are not allowed).

3. \({23 \choose 4}\) sodas (order does not matter and repeats are allowed; 4 stars and 19 bars).

4. \(20^4\) sodas (order matters and repeats are allowed; 20 choices 4 times).