MindYourDecisions puts a dollar-book riddle under the microscope
Presh Talwalkar uses algebra, a visual model and puzzle history to explain why half the price isn't half a dollar.
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The $1 Book Riddle That Breaks Everyone's Brain
Things we can learn from the video
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- 0:00The riddle asks for a book's price when it costs $1 plus half its own price.
- 3:31The equation b = 1 + b/2 gives a price of $2.
- 4:06A bar model shows that the dollar accounts for the other half of the book's price.
- 6:32Talwalkar traces the puzzle through The Moscow Puzzles and an earlier Russian text.
- 7:44He addresses objections about the meanings of "costs" and "price."
How much can there be to explain about the price of a book? In Presh Talwalkar's hands, enough for an algebra lesson, a diagram and a detour into decades-old Russian puzzles.
MindYourDecisions posted nothing new this week, but "The $1 Book Riddle That Breaks Everyone's Brain" is its strongest daily draw right now. Its question sounds almost too small to cause trouble: a book costs $1 plus half its price. The tempting answer is $1.50. The correct answer is $2, because the extra half refers to the book's entire price, not the dollar mentioned first.
Talwalkar doesn't stop at solving the equation. He shows the same reasoning with a bar model, then tackles the objection that the wording itself is the problem. His own polls make that detour relevant: a substantial share of respondents dismissed the question as confusing rage bait. He also traces versions of the puzzle through Boris A. Kordemsky's The Moscow Puzzles and an earlier Russian text. Apparently, this particular argument didn't need the internet to get started.
Elsewhere in the back catalog, "A Geometry Puzzle That Looks Impossible At First" asks viewers to find a square's area from equal-area rectangles, while "An SAT Question That Most Students Get Wrong" remains another active draw.
The channel added about 850,000 views over the week, with its subscriber count unchanged. Daily viewing is now roughly half its usual pace. Among nearby educational channels, Computerphile is enjoying a pronounced daily lift, while mathantics is a little below its usual level. For MindYourDecisions, the book riddle is the busiest of its older lessons right now.
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💡 Test your knowledge
What is the correct book price in Talwalkar's riddle?
Half of $2 is $1, so $1 plus half the book's price equals $2.