U2 has a concert that starts in 17 minutes and they must all cross a bridge to get there. All four men begin on the same side of the bridge. You must help them across to the other side. It is night. There is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either 1 or 2 people, must have the flashlight with them.
The flashlight must be walked back and forth. It cannot be thrown and other tricks like that are not needed to solve the problem. The solution is simply a matter of allocating resources in a certain order. Each band member walks at a different speed. A pair must walk together at the rate of 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 elapsed when they get to the other side of the bridge. If Larry then returns with the flashlight, a total of 20 minutes have passed and you have failed the mission.
This is one of my favorite brain teasers and I want to give you the satisfaction of figuring it out on your own. If you’re having a hard time, here’s a hint: There is a valid answer that doesn’t require tricks like throwing the flashlight or shining it backwards or having some other means of moving the flashlight.
There’s an assumption people often make that keeps them from solving this. Two members cross the bridge each time, but neither one of the two who crossed necessarily need to return. Think about how that would be possible. If you’re still stuck, use objects to simulate their movements. Use whatever you have laying around – pens, paper, erasers – and move them back and forth. Good luck!
You are the bus driver. At your first stop, you pick up 29 people. On your second stop, 18 of those 29 people get off, and at the same time 10 new passengers arrive. At your next stop, 3 of those 10 passengers get off, and 13 new passengers come on. On your fourth stop 4 of the remaining 10 passengers get off, 6 of those new 13 passengers get off as well, then 17 new passengers get on. What is the color of the bus driver’s eyes?
Three travelers register at a hotel and are told that their rooms will cost $10 each so they pay $30. Later the clerk realizes that he made a mistake and should have only charged them $25. He gives a bellboy $5 to return to them but the bellboy is dishonest and gives them each only $1, keeping $2 for himself. So the men actually spent $27 and the bellboy kept $2. What happened to the other dollar of the original $30?
There is no missing dollar from the original $30 because after getting $1 back, the three travelers had paid a total of $27 for their room ($9 each), not $30. Out of that $27, the hotel has $25 and the clerk kept the remaining $2. If you still want to work from the original $30, the travelers have $3, the hotel has $25 and the bellboy has $2. The misleading part is adding the bellboy’s $2 to the $27, when in fact it should be subtracted.
Chuck and Ruby were going to meet at a hotel for their anniversary dinner, but Ruby didn’t show. Chuck was angry and left her a passive aggressive message on their kitchen table in the form of fifteen matchsticks spelling “hotel” and went to bed. When Ruby got home and saw the matchsticks, she removed one and went to bed. When Chuck woke up the next morning and saw Ruby’s new message, he realized his mistake. Which stick did Ruby remove and what was the new message?
Ruby had removed the top of the T and the new message could be seen upside down from where Chuck sat at his breakfast of sadness and anger. What he saw was 7 3 1 0 4, or 7/31/04, the date of their anniversary. In his excitement, Chuck had gone to the restaurant a day early, on July 30th. All was forgiven by both parties and Chuck and Ruby had a wonderful dinner together. They also promised to buy a whiteboard for the kitchen so they wouldn’t have to use matchstick messages ever again.
Jim and his wife Patty were sitting in bed together one evening while a thunderstorm raged outside. After a bolt of lightning followed by a loud clap of thunder, the lights went out. Jim stopped reading and went to sleep, but Patty continued reading in the dark. How did she do it?
Patty is blind and was reading a Braille book so she didn’t need the light to begin with. Of course this also meant she didn’t know Jim snuck downstairs to get some cookies, but we’ll just keep that quiet.
Shawn and Kyle are bunk mates in prison and are desperate to escape. There is an unbarred window high above them, but the walls are smooth and it’s too high for them to reach even when standing on each other’s shoulders. Their cell has no furnishings other than a toilet and even when standing on the toilet and each other’s shoulders, they can’t reach the window.
They’ve tried digging through the dirt floor but the wall extends 50 feet below. How could escape through the window?
They could dig down with their hands, but it would take too long to dig 50 feet down. Instead, they could pile the dirt they dig up to give them enough height to reach the window. If they put the toilet seat down, they could pile the dirt on top, then get on each other’s shoulders to reach the window. That would mean only one of them would be able to get out. The remaining prisoner could either continue piling dirt to account for the missing guy or the escaped prisoner could come back with a rope to help his mate escape.
On the sixth of May in the year 1978 at exactly thirty-four minutes past noon, a most extraordinary event occurred. This singular occasion will probably never be witnessed by anyone who was alive at that time. What happened?
The time and date was 12:34 5/6/78, counting from one to eight. The next time this event will occur is 12:34 6 May 2078. Unless someone alive in 1978 lives to be over a hundred, they won’t be alive when it happens again.
