Got No Pictures To Show Ya, But See If This Teases Your Noodles.

[RipRocK]

This question was given to me in an oral technical question session I had to take during an interviewing process for the very first company I went to work for. I had three minutes to solve it and did it with like only 15 seconds to go. Here it goes:

There are 4 people who are trying to cross a river, but there's only one paddle boat which can accomodate only 2 people at a time. Given that it takes 1, 2, 5 and 10 minutes respectively for those 4 to cross the river, find a way that will have all of them on the other side of the river in 17 minutes.

If 2 people are travelling together on the boat, then the travel time will always be the greater of the 2 people. For eg., if 2 minute person and 10 minute person travel together, the time to cross the river will be 10 minutes.

So, one example I can give you is, 1 & 10 go over to the other side and 1 comes back (total of 11 minutes so far). Then 1 & 5 go over and 1 comes back (total of 17 minutes so far). Then, finally, 1 & 2 go over and the total ends up being 19 minutes. Obviously, it's over 17 minutes, so it's the wrong answer. Good Luck!

[xyzzy]

Easy! Just vote the 10 minute person off the island because they were weak and hurting the tribe anyway. Then it's 5&1, 1 comes back, 1&2 go over and you end up with 8 minutes.

Now, where's my cookie?

Chris

[AgPilotOwner]

Send the 1 minute and 2 minute people over. (2 minutes)
Send the 1 minute person back. (1 minute)
Send the 5 minute and 10 minute people over. (10 minutes)
Send the 2 minute person back. (2 minutes)
Send the 1 minute and 2 minute people over. (2 minutes)

17 minutes!

[RipRocK]

Originally posted by xyzzy
Easy! Just vote the 10 minute person off the island because they were weak and hurting the tribe anyway. Then it's 5&1, 1 comes back, 1&2 go over and you end up with 8 minutes.

Now, where's my cookie?

Chris

Sorry, wrong answer, but I like the way you think, which leads me to this story.

Billy's in his kindergarten class and his teacher, Mrs. Anderson, is teaching math. She asks him a question, "Billy, if there were 5 birds sitting on a fence and the farmer shot one of them, how many birds would be left?" Billy answers, "None." Mrs. Anderson was rather perplexed by his answer and told him to explain his answer, to which Billy replied, "Well, if one bird gets shot, the rest of the birds would fly away as quickly as they could." Mrs. Anderson smiled and said, "The correct answer is 4, but I like the way you think."

Then, Billy asked Mrs. Anderson, "If there were 3 ladies eating a popsicle and the first woman was just vigorously munching down on it, the second woman was just barely licking it and the third woman was taking the whole thing deep into her mouth and then taking it out, which one would be the married one?" While blushing, Mrs. Anderson replied, "I guess the third one would be the married one." And Billy said, "Nope, the one with the wedding ring would be the married one, but I like the way you think."

[RipRocK]

Originally posted by AgPilotOwner
Send the 1 minute and 2 minute people over. (2 minutes)
Send the 1 minute person back. (1 minute)
Send the 5 minute and 10 minute people over. (10 minutes)
Send the 2 minute person back. (2 minutes)
Send the 1 minute and 2 minute people over. (2 minutes)

17 minutes!

I actually had answered with the 2 minute guy coming back first, not the first one. Don't ask me why, the permutations I performed in my head just ended up that way.