A Microsoft Interview Question (aka basic Bayes' Theorem)

[alThor]

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To me it shows how superior the Microsoft style of interviewing (solve these problems now, please) is to a more traditional style

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Since I can't stand seeing M$ being credited with anything, let me point out that consulting firms (e.g. McKinsey) have used this style of interview for quite awhile.

alThor

[SomethingClever]

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This problem is flawed; anyone you would play this game with would not be your freind. So your prolly on acid and playing it w/ the lamp and a banana.

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DING DING DING!

[theTourne]

I like the following riddle. It took me a while.

There are 8 people who need to cross a river. They have a boat, but it only holds two at a time. The people are:
Father
Mother
2 Sons
2 Daughters
Policeman
Thief

Due to the disfunctionality of the family, and the fact that the thief is a bad, bad man; the following three rules most be observed at all times.

1. The thief cannot be with any members of the family unless the policeman is present.

2. The mother cannot be with either of the sons unless the father is present.

3. The father cannot be with either of the daughters unless the mother is present.

Finally, since the current is strong (and the thief isn't to be trusted) only the father, mother or policeman may row the boat.

Can you get them all across?

[Blackjack]

Haven't read any of the other replies.

If he has fired it and there was no bullet. That means he landed in any of 4 places. 1/4 of those places will result in the next shot fired meaning bye bye for you.

If you spin it again, there are 2 slots that will kill ya out of 6 possible.

So the answer is... Shoot it again if you wanna maximize your chances of staying alive by 8%.

[pudley4]

[ QUOTE ]
I like the following riddle. It took me a while.

There are 8 people who need to cross a river. They have a boat, but it only holds two at a time. The people are:
Father
Mother
2 Sons
2 Daughters
Policeman
Thief

Due to the disfunctionality of the family, and the fact that the thief is a bad, bad man; the following three rules most be observed at all times.

1. The thief cannot be with any members of the family unless the policeman is present.

2. The mother cannot be with either of the sons unless the father is present.

3. The father cannot be with either of the daughters unless the mother is present.

Finally, since the current is strong (and the thief isn't to be trusted) only the father, mother or policeman may row the boat.

Can you get them all across?

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Here's a link to a flash version

Hint: <font color="white"> it takes 9 trips across </font>

[SumZero]

I like this question on conditional probability because it quickly sees if the person has an intuitive sense of probability. And, since it is a pretty easy question IMHO, it has a nice followup question which could be useful in a situation where the person got it right (although I'm not sure logic/math questions are the best questions to ask potential programming interviewees, I'd much prefer asking them to put real code on the board).

So you ask the question about maximizing the probability of survival through the next round. The person thinks for 5 to 10 seconds and says 3/4 chance to survive if you don't spin versus 2/3 chance if you do spin, so you should not spin if you want to win.

Followup question: Assume you are now the first player. You pulled the trigger and got a click. Your opponent didn't spin, pulled the trigger and got a click. The gun is now handed to you (unspun). You are faced with the decision to spin the chambers and shoot or just straight up shoot the gun as is. Does it matter what your strategy should be?

[DQPaulie]

I would say our strategy matters. If we look at the situation now, we have a 2/3 probability of survival either way. Our odds are the same either way, but are the situations to follow the same? If our opponent knows all the same odds as we do, we have to pull the trigger unspun. Reason is if we survive we leave hime with a 1/2 chance of survival if he just pulls the trigger, so he will spin to better his probability of survival to 2/3 and if he misses we get the 3/4 probability to survive again. If we spin we get the same odds as not spinning, but then leave him with the favorable odds of 3/4 . We would rather have the 3/4 odds if we get that far.

[Slow Play Ray]

I didn't post an response (already too many correct answers, no point), but I did get the right answer. Since then, I have been asking everyone I know this question, and I am in awe of how many got it wrong. My boss is the ONLY person I asked to get it right, with the right reasoning, on the first attempt.

GREAT post Ed!

[AviD]

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Does it matter which one you choose? If it does, why?

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My answer would be no it doesn't matter which one you choose...you're an idiot for playing Russian Roulette with a friend (no less). Just keep squeezing until it goes off, but be sure to tell your "friend" (before you start) to follow suit after the first one goes off. He shouldn't have to wait too long for his turn.

Sounds like a fun interview...is this Microsoft's way of "thinking outside the box"? [img]/images/graemlins/grin.gif[/img]

[TomCollins]

ARG, I got it, but now I can't remember how I started.