11. Logic Puzzle: Let’s pretend we’re on the metric system and use kilograms instead of pounds to give us a starting base number of 100. Four people (Alex, Brook, Chris and Dusty) want to cross a river in a boat that can only carry 100kg. Alex weighs 90kg, Brook weighs 80kg, Chris weighs 60kg and Dusty weighs 40kg, and they have 20kg of supplies. How do they get across?
Answer: There may be a couple variations that will work, but here’s one way: Chris and Dusty row across (combined 100kg), Dusty returns. Alex rows over, and Chris returns. Chris and Dusty row across again, Dusty returns. Brook rows across with the supplies (combined 100kg), and Chris returns. Chris and Dusty row across again.
12. Logic Puzzle: This famous river crossing problem is known as the “bridge and torch” puzzle. Four people are crossing a bridge at night, so they all need a torch—but they just have one that only lasts 15 minutes. Alice can cross in one minute, Ben in two minutes, Cindy in five minutes and Don in eight minutes. No more than two people can cross at a time; and when two cross, they have to go at the slower person’s pace. How do they get across in 15 minutes?
Answer: Alice and Ben cross first in two minutes, and Alice crosses back alone with the torch in one minute. Then the two slowest people, Cindy and Don, cross in eight minutes. Ben returns in two minutes, and Alice and Ben return in two minutes. They just made it in 15 minutes exactly.
13. Logic Puzzle: A bad guy is playing Russian roulette with a six-shooter revolver. He puts in one bullet, spins the chambers and fires at you, but no bullet comes out. He gives you the choice of whether or not he should spin the chambers again before firing a second time. Should he spin again?
Answer: Yes. Before he spins, there’s a one in six chance of a bullet being fired. After he spins, one of those chances has been taken away, leaving a one in five chance and making it more likely a bullet will be fired. Best to spin again.
14. Logic Puzzle: Same situation, but two bullets are put in consecutive chambers. Should you tell the bad guy to spin the chambers again?
Answer: No. With two bullets, you have two chances in six (or one in three) to get hit with a bullet before he fires the first time. Because we know the previous round was one of four empty chambers, that leaves four positions the gun could now be in, with only one followed by a bullet; therefore leaving you with a one in four chance the second round will fire. Since one in four is better odds than one in three, he shouldn’t spin again.
15. Logic Puzzle: This one could also fall in the lying/truth category. A man is caught on the king’s property. He is brought before the king to be punished. The king says, “You must give me a statement. If it is true, you will be killed by lions. If it is false, you will be killed by trampling of wild buffalo. If I can’t figure it out, I’ll have to let you go.” Sure enough, the man was released. What was the man’s statement?
Answer: “I will be killed by trampling of wild buffalo.” This stumped the king because if it’s true, he’ll be killed by lions, which would render the statement not true. If it’s a lie, he’d be killed by wild buffalo, which would make it a truth. Since the king had no solution, he had to let the man go.
Leave a Reply