Tanya Khovanova stands out in the field of recreational mathematics. She maintains a popular blog and operates a website called Number Gossip, where users can input a number to learn intriguing facts about it. Khovanova has co-authored her debut book, Mathematical Puzzles and Curiosities, alongside Ivo David and Yogev Shpilman. The volume offers a collection of innovative puzzles and fresh takes on classics. Below are three notable examples.
1. Naval Strategy
As a naval commander overseeing a critical operation, you face two options:
a) Dispatch one vessel with a P percent likelihood of succeeding.
b) Send two vessels, each with a P/2 percent chance of success.
The mission succeeds if at least one vessel prevails. Which choice provides the better odds?
2. Distinguishing Oracles
You encounter two oracles, Randie and Rando, who respond to questions with yes or no. Randie gives random answers to every query. Rando randomly chooses to be truthful or deceptive for each question and replies based on that decision. Can you differentiate between them? If yes, how?
3. Faulty Arithmetic
Johnny’s assignment involves subtracting 5489 from 5548, yielding 59. He simplified by canceling out 548, resulting in 59. He tried the method again with a subtraction like XXYZ minus XYZW, where X, Y, Z, and W are different digits, and it produced XW. How many digits in this new problem match those in the original (such as X equaling 5, Y equaling 4, Z equaling 8, or W equaling 9)?
Solutions will appear at 5 p.m. UK time. Avoid sharing answers.
Mathematical Puzzles and Curiosities, by Ivo David, Tanya Khovanova, and Yogev Shpilman, is available from World Scientific. The puzzles have been adapted for this feature. This column has presented puzzles every other Monday since 2015. Suggestions for future puzzles can be sent via email.
