A few days ago I reviewed How Would You Move Mount Fuji, a great new book about the logic puzzles often used in technical interviews. I received a lot of feedback - thanks! - and some interesting meta-reviews (reviews of my review). My favorite meta-review was by Chris Lightfoot. He was pretty critical - as he put it "such pontifications irk me" - but the reason I liked it was that he gave a different and better answer to the $21 question.
You may remember this question goes as follows:
I called this the worst question in the book, based on the fact that it has no answer. I went on to say:
So it turns out that this question does have an answer! Chris writes:
Excellent! When I read this question in the book it was described as having no answer, and it never occurred to me that the book was wrong, and that this question really does have an answer. I believe whoever first posed this question was looking for Chris' answer; this is a classic "thinking out of the box" test. Any candidate is going to do the algebra and conclude that there is no integer solution in dollars. Will they then consider shifting units to cents? Very interesting.
I don't know what my reaction would have been if the question had been posed as answerable. Would I have thought to give the answer in cents? Don't know. But when the book stated that the question was not answerable, I took their word for it. Bad Ole.
Since I'm following up on the review, I wanted to mention a couple of other puzzles which were emailed to me as great questions: