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Book: How Would You Move Mount Fuji

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This book is targeted at people who are preparing for an interview. Although it is a book about interview puzzles, the puzzles take up very little of the book. Most of the book is dedicated to interview guides (for the interviewer and interviewee) and the history of the logic puzzle, from its use in IQ tests to its adoption by job interviews. The history was a little bit interesting to me, mostly because it talked about Shockley, and it also happened to mention Jim Gibbons name, which made my world a little bit smaller. The main reason I picked this book up, though, is that I happen to like the puzzles that they give you during interviews, and I'm too lazy to find them on the Internet.

There are plenty of Fermi estimation questions in the book (the title of the book ends up being one). Fermi estimation questions ask you to estimate the value of something you don't know, like the number of redheads in Ireland. When I was in high school, we had an entire unit on this in chemistry. My chemistry teacher introduced the unit by telling the anecdote of Fermi at one of the nuclear bomb tests. As the shockwave approached, Fermi threw some scraps of paper into the air and watched their deflection. From this observation, he came up with an estimate of the megatons of the explosion that was reasonably accurate.

It's really not much use searching for examples of Fermi type problems; pretty much any type of estimation will serve as practice. Although it's nice to have estimation skills, as puzzles I find these a bit boring.

Another class of problems they have are design-type questions, where you get asked how you would design/build some sort of item. While I think these are good interview questions, as they allow the interviewer and interviewee to interact back and forth, I don't find them too interesting to solve in my freetime.

The last class of problems, logic problems with actual solutions, are the ones that I was shooting for when I got the book. There are some good ones in this book which made it worth the price of admission. Here are some of my favorites:
- 5 pirates have 100 gold coins to divide. The senior pirate proposes how to divide the coins, and the pirates then get to vote. If at least half of the pirates agree to the proposal, the division is made; otherwise the senior pirate is killed and the process is repeated. If you are the senior pirate (pirate #5), what should you propose?

- There is a village of 50 husband and wife couples. All of the husbands have been unfaithful. The wives know when men other than their own husbands have cheated, but they don't know about their own husbands fidelity. If a wife can prove that her husband has cheated, then she is required by law to kill him. Also, all of the wives are blessed with Spock-like logic skills. One day, the queen stops by and announces, "at least one of your husbands has been unfaithful." What happens?

- How many points are there on the globe where, by walking one mile south, one mile east, and one mile north, you reach the place where you started?

- Count in base negative 2 (doesn't have a "correct" solution)

- You have five jars of pills. Normal pills weight 10 grams, while poisonous pills weight 9 grams. One of the jars is filled with poisonous pills. Measuring once on a scale, how do you find the poison jar?

Comments (5)


I have an answer for the last one. Naturally, this is a SPOILER if someone else wants to think about it, so here's some space...


If I'm allowed to take pills out of each bottle, then I'll take one from bottle A, two from bottle B, three from bottle C, four from bottle D, five from bottle E, and weigh the entire lot. I'll be able to conclude from the weight which bottle has the pills. To wit:

Total weight is 149g -- Bottle A
Total weight is 148g -- Bottle B
Total weight is 147g -- Bottle C
Total weight is 146g -- Bottle D
Total weight is 145g -- Bottle E

Asymmetry, man.


Of course, my knee-jerk answer to the title of the book is "tactical nuclear weapons." I don't think that's what they're looking for.


You can optimize your answer by not measuring one of the bottles. Saves you a tiny bit of effort.

The title of the book is strange, as the actual wording of the problem in the book is more akin to, "How long would it take to move Mt. Fuji." My snotty answer to that would be "one day": drill a hole, stick some dynamite in, blow it up, point at the ground shaking, and say, "it moved."


I have an adaptation to the Mount Fuji question. You have two mountains and you want to switch them. How would you go about moving them?


ACS, simple rename both the mountains.. :)

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This page contains a single entry from kwc blog posted on April 27, 2004 11:09 PM.

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