How Do You Fight a Horse-sized Duck? : And Other Perplexing Puzzles from the Toughest Interviews in the World (9780861540082) by Poundstone William

Author:Poundstone, William
Language: eng
Format: epub
ISBN: 9780861540082
Publisher: Simon & Schuster
Published: 2021-01-15T00:00:00+00:00

Example: I’m interviewing on Tuesday, July 12, 2022. It’s not a leap year. There will be 3 leap years in the coming 10 years (2024, 2028, and 2032). The 2032 leap year counts, as July 12 is after February 29. The leap years advance the day of the week 3 days on top of 10 years’ worth of annual advances, for 13 days total. Subtract 7 to get a net advance of 6 days. In 10 years (2032), therefore, July 12 will be 6 days ahead of Tuesday, meaning a Monday.

Don’t forget the second part of the question: How confident are you of your answer?

Research shows that people tend to be overconfident of their knowledge, skills, or accuracy. In a notorious example, a 1981 study found that 93 percent of drivers believed their driving skills to be better than average.

Predictive models are the lifeblood of the insurance, financial, and consulting industries. It is not just important for models to be accurate; it is necessary to know how accurate they are. All models fail, sometimes. Countless companies have gone under because some very smart people were too sure their predictions were right.

Even when you’re as sure as sure can be, there is some nonzero chance you’ve made an error. In answering this question, you should acknowledge that. Having 99 percent confidence in a mental calculation — under the stress of a job interview, no less — would be impressive. Claiming 100 percent confidence would be unrealistic.

? You have two well-shuffled decks of cards. One is a regular deck of 52 cards. The other is a half-deck with just 26 cards (the hearts and spades only). You are to pick a deck and then draw two cards from it. If the cards are the same color (red or black), you win. Which deck would you choose?

Also: Suppose there were a third deck, consisting of 26 cards drawn randomly from a full deck. Which deck would you now choose?

Blackjack players know that decks are finite, and this has consequences. Drawing an ace depletes the supply of aces remaining in the deck. This decreases the chance of drawing another ace.

The same principle applies here. Suppose you draw a card from the regular deck. It’s red. That leaves 25 red cards remaining in the deck (which now has 51 cards). The chance of drawing a second red card is 25/51. This is about 49 percent, less than the 50 percent that applied for the first card.

The half-deck of 26 cards is smaller and more affected by each card drawn. After selecting a first card, there will be only 12 cards of the same color in the remaining 25 cards. The chance of getting another card of the same color is 12/25, or 48 percent.

You should therefore prefer the full deck to the half-deck. It’s not a huge difference, but there is one.

The follow-up question asks about a half-deck of 26 cards drawn randomly from a full deck of 52. Because it’s random, there is no guarantee of an even split of colors.

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