Its fun to visualize the symmetric differences of sets of banknotes that Alice and Bob has. For a given set of five bank notes, I calculated all the symmetrical differences of Alice and Bob's bills for all 100x100 possible amounts. I assigned a color to each of the 32 possible symmetrical differences, and plotted a scatter plot. I plotted white for those combinations where Alice and Bob has exactly the same set of bills. It gives a nice quilt like patterns. One can enter 5-bills comma separated in the text box and hit "Repaint" to see how the the distribution of bills look like. Try will few examples like "1, 5, 10, 20, 50", "1, 4, 20, 40, 80", etc. It also spits out the probability that we were looking for in the problem.

Solutions to Ponder This 2019 September challange:
Enter five distinct bills between 1 and 99, comma separated (ex: "1, 5, 10, 20, 50"):