Thursday morning brain strain...

[Greatwhite]

Usually after hump-day, I can't think about anything but the weekend ahead.  Someone on Facebook posted this problem, and now my brain hurts after solving it.

Four people are being pursued by a menacing beast.  It is nighttime, and they need to cross a bridge to reach safety.  It is pitch black, and only two can cross at once.  They need to carry a lamp to light their way.  The first person can cross the bridge in no less than 10 minutes, the second in 5, the third in 2, the fourth in 1 minute.  If two cross together, the couple is only as fast as the slowest person.  A fast person cannot carry a slow one - if the 10 minute and 1 minute person go together, it will take 10 minutes.

The person or couple crossing the bridge needs the lamp for the entire crossing and the lamp must be carried back and forth across the bridge (no throwing).  If all don't get completely across the bridge in less than 18.5 minutes, whoever is on the bridge or left behind will be eaten by the beast.  Is it possible to get them all across?

I know the answer, after working it out in my head (incorrectly) for HOURS before the answer came to me.

[Hookup]

The trick here is to work on the weakness not the strength.

I admit, it is something that I had seen a long time ago, and it did get me back then so I've always remembered the solution.

[Greatwhite]

The trick here is to work on the weakness not the strength.

I admit, it is something that I had seen a long time ago, and it did get me back then so I've always remembered the solution.

Yeah, I remember the problem - probably saw it the same place you did.   I am 90% sure that I got it wrong back then, and didn't remember seeing the right answer.

Here's a hint to anyone trying to solve this..  It doesn't have to be the same guy to escort people across. (that's where I went wrong)

[az]

hmmm, is there a 'throw the beast off the bridge' option? my brain hurts already.

[Greatwhite]

As long as I'm faster than the slowest person - I'm happy.  OR, I could just push down someone faster than me and still be safe.  This whole "getting everyone across safely" thing sucks.

[Hookup]

The best hint i can give is

1) work the problem... the problem is slow people...

Anything else will give away the solution I think.

[Feivel]

Boo ya 17 minutes :-)      kinda hard to think and work but i got it :-)  19 for the longest time ....

[Jkelley]

IGNORE COUPLES...lmao
I gots it

[Greatwhite]

Boo ya 17 minutes :-)      kinda hard to think and work but i got it :-)  19 for the longest time ....

14 internet points for Feivel for figuring it out.    I always had the 1 minute guy escorting people back and forth across the bridge because he's fastest to return.  Slow & steady wins the race here, I guess.

[Darth]

I just googled it it was easy

[Feivel]

Cheater :-)     

Did anyone get the 18.5... I was like well i could drop 5 half way but it would fill itself again once you come back for it lol. But yeah. My clue is start small :-)

[Jkelley]

No way you can get 18.5 I don't think you can get anything faster than 17?

[Hookup]

I think that 17 is best time...  It's all i could get.

the 1/2 seems only achieved if you bend some rules somehow... all numbers are round.

[dpatte]

17 looks good. I was convinced it was 19 for about 5 minutes, but persisted until i found 17. Its a good lesson that forces you to retest your assumptions!