Re: Puzzle

From: Bill Jones <jones_at_no.spam.please>
Date: Fri Dec 12 1997 - 20:23:52 CST

>When I find out what the answer is I will forward it to the list.

Okay, how about this.

It would seem at first glance that the puzzle can't be solved,
since each trip across the bridge deposits one person on the other
side, and the sum of times walking individually is already 18 minutes,
never mind return trips carrying the flashlight.

Well, almost. Consider the following:

1. Bono and Edge cross, 2 minutes, total 2.
2. Bono or Edge returns, 1 or 2 minutes, total 3 or 4.
3. Adam and Larry cross, 10 minutes, total 13 or 14.
4. Edge or Bono returns, 2 or 1 minutes, total 15.
5. Bono and Edge cross, 2 minutes, total 17.

The hole in the pseudoproof of impossibility is that one of the
crossings will deposit two people for good on the other side.
The trick is to arrange things such that the slow guys go together
and don't return, leaving slack for relaying the flashlight.
That means they have to cross in the middle of the process,
and then the rest falls into place.

Because I don't care about U2 punctuality or Microsoft coder jobs,
y'all feel free to use this at the interview, but just agree that I can
have your stock options.

>>Date: Fri, 12 Dec 1997 14:04:28 -0600
>>From: "Peter Hardie" <>
>>X-Mailer: Mozilla 4.04 [en] (Win95; U)
>>To: Chris and Linda Morgan <>
>>Subject: Puzzle
>>"U2" have a concert that starts in 17 minutes and they must cross a
>>to get there. All four men begin on the same side of the bridge. You
>>help them across to the other side. It is night. There is one
>>A maximum of two people can cross at one time. Any party who crosses,
>>1 or 2 people must have the flashlight with them. The flashlight must be
>>walked back and forth, it cannot be thrown, etc. Each band member walks
>>a different speed. A pair must walk together at the slower man's pace:
>>Bono - 1 minute to cross
>>Edge - 2 minutes to cross
>>Adam - 5 minutes to cross
>>Larry - 10 minutes to cross
>>For example: If Bono and Larry walk across first, 10 minutes have
>>when they get to the other side of the bridge. If Larry then returns
>>the flashlight, a total of 20 minutes have passed and you have failed
>>There is no trick behind this. It is the simple movement of resources in
>>the proper order. There are two known answers. This is based on a
>>Microsoft gives to all prospective employees. Note: Microsoft expects
>>to answer this question in under 5 minutes!
>Chris and Linda Morgan
Received on Fri Dec 12 20:23:52 1997

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