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Jagular

Saturday, May 07, 2005

A harder word problem

Here is another classic word problem. It's a bit harder than the first one. Don't expect to figure it out on the first try. Or the second try. If you work by trial and error, you could, theoretically, get the answer, but I haven't ever seen anyone actually get it that way. The easiest way to figure it out is to try it a couple of times and then stop and think about it and keep asking what went wrong.
Ok, here it goes:

Four explorers are out hiking a trail at night. They come across a deep ravine with a rickety old rope bridge with half rotten wooden slats. They only have one flashlight among them. Because it is so dark and the bridge is so old, only two of them can get across safely at a time. Also, because of varying degrees of agility and bravery, they can each cross at different speeds.
The first guy can get across the bridge in one minute.
The second guy can cross it in two minutes.
The third guy in five minutes.
And the fourth guy in ten minutes.
If two people are crossing together, they have to travel at the slower person's pace.
So, for example, if they all want to cross the bridge, they could do it as follows:

Person number one and two go across together. (takes two minutes)
guy number one comes back across with the light (takes one more minute. three total so far)
guy number one and three go across. (takes five more minutes, total of eight)
number one goes back across with the light (add another minute, total of nine.)
number one and number four cross in ten minutes (grand total of nineteen minutes)

So here is the question...........................How can they all cross in only seventeen minutes?

There are actually two solutions for it. Good luck.

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