Without running anything, say how many subsets there are for lists of 5, 10 and 20 items…

Plan. Each item is in or out, so a list of $n$ items has $2^n$ subsets. The arrangements of $n$ different letters are $n!$.

For 5 and 10 items the subsets are 32 and 1024. For 20 items, 1 048 576. The arrangements: 120 for 5 letters, 40 320 for 8 letters.