And that, he thought, was a better formula than any in the book.

He typed his answer: 392 cm². Then, curious, he scrolled further. The annotations continued. Next to the chapter on probability, a note read: "Life is not a fair die. But this question is. P(>4) = 2/6 = 1/3." Next to a bar graph about ice cream sales, someone had written: "Vanilla wins. It always wins."

He worked through the problem, but something felt off. In the PDF, next to the answer box, a faint, penciled note read: "Mr. Jensen’s class: The answer in the back is wrong. It’s 392, not 376. Trust the formula."