On the subject of memory: The section on pi has two mistakes, alas, which I found to be particularly unfortunate. One of the mnemonic poems has a misprint "never more" instead of "nevermore", leading to a knock-on error in the digits beneath it, and there's a second error in the digits where the word "passed" in the poem is counted incorrectly as 5 letters.
Unfortunately, that's what I first memorized pi from. I had to re-learn the correct decimal expansion.
As for the 66th puzzle, there's a clear inspiration for slipping that sort of question in and seeing if anyone who doesn't know better actually comes up with an answer. It's interesting to note that some of the items have indeed been answered since 1985. I wonder whether M. Devi had heard Robert Schuller's tale, which was in wide circulation by 1983.
* https://snopes.com/fact-check/the-unsolvable-math-problem/