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!
Eat (8) flush (plus) to (2) my nose (minus) tree (3) times (times) for (4) they buy dead by (divided by) too (2).
There are two answers depending on whether you calculate as you read or calculate the entire solution at the end. 8 + 2 = 10, – 3 = 7, x 4 = 28, / 2 = 14 or 8 + 2 – 3 x 4 / 2 = 10 – 6 = 4
Hester goes out for an afternoon bicycle ride. She rides for one hour at five miles an hour, then three hours at four miles an hour and finally two hours at seven miles an hour. How many miles did she ride in total?
On a dark, stormy Halloween night, four kids named Luke, John, Sarah and Bob walk into a haunted house during a blackout. Only one can escape. They take a staircase to the second floor, a trapdoor on the left, then go up the ladder to the right, followed by a 28-foot slide to the basement through the mouth of a Giant Panda. In one corner of the murky cellar is a chainsaw, a dagger, a rope with a noose and an electric chair. Written on the wall in blood are the words, “Only one will survive – choose your death!” Bob takes the rope, Sarah picks up the dagger, John chooses the chainsaw and Luke uses the chair.