There are 25 mechanical horses and a single racetrack. Each horse completes the track in a pre-programmed time, and the horses all have different finishing times, unknown to you. You can race 5 horses at a time. After a race is over, you get a printout with the order the horses finished, but not the finishing times of the horses. What is the minimum number of races you need to identify the fastest 3 horses?
I was suggested this puzzle via email by Terry Stickels. This is also a popular interview question at tech companies like Google. See a list of all sources in my blog post for this video:
https://wp.me/p6aMk-58P
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My Books
“The Joy of Game Theory” shows how you can use math to out-think your competition. (rated 4/5 stars on 34 reviews)
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“The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias” is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 4.6/5 stars on 3 reviews)
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“Math Puzzles Volume 1” features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.4/5 stars on 13 reviews.
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“Math Puzzles Volume 2” is a sequel book with more great problems. (rated 4.5/5 stars on 6 reviews)
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“Math Puzzles Volume 3” is the third in the series. (rated 4/5 stars on 6 reviews)
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“40 Paradoxes in Logic, Probability, and Game Theory” contains thought-provoking and counter-intuitive results. (rated 4.4/5 stars on 13 reviews)
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“The Best Mental Math Tricks” teaches how you can look like a math genius by solving problems in your head (rated 4.8/5 stars on 5 reviews)
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“Multiply Numbers By Drawing Lines” This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 4.4/5 stars on 5 reviews)
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