Brain teasers and answers

Question 1: 

By moving one of the following digits, make the equation correct. 62 - 63 = 1 

Answer: 2⁶ - 63 = 1 (In other words, 2x2x2x2x2x2, which equals 64) 

Question 2: 

You have a fox, a chicken and a sack of grain. You must cross a river with only one of them at a time. If you leave the fox with the chicken he will eat it; if you leave the chicken with the grain he will eat it. How can you get all three across safely? 

Answer: Take the chicken over first. Go back and bring the grain next, but instead of leaving the chicken with the grain, come back with the chicken. Leave the chicken on the first side and take the fox with you. Leave it on the other side with the grain. Finally, go back over and get the chicken and bring it over. 

Question 3:   

You have 12 black socks and 12 white socks mixed up in a drawer. It's early in the morning and you don't have any light to see the colors. How many socks must you pull out (blindly) to be sure of getting a matching pair? 

Answers: 3 socks. If the first sock is black, the second one could be black, in which case you have a matching pair. If the second sock is white, the third sock will be either black and match the first sock, or white and match the second sock. 

Question 4: 

What is special about the following sequence of numbers?
                    8 5 4 9 1 7 6 10 3 2 0
Answer: The numbers are in alphabetical order.
(eight, five, four, nine, one, seven, six, ten, three, two, zero) 

Question 5: 

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? 

Answer: Nothing. The 3 travelers paid a total of $27, making $25 for the hotel and $2 for the clerk. There is no missing $1.

Question 6: 

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?
Answer: The eye color of the reader of this problem. The first sentence is the key: "You are the bus driver".

Question 7: 

A rooster lays an egg at the very top of a slanted roof. Which side is the egg going to roll off on? Answer: Neither, roosters don't lay eggs.

Question 8: 

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. 

Answer: Let’s name the as A,B,C & D and let’s assume that they take 1,2,5 and 10 minutes respectively. Here is how they should cross the bridge. 

ABCD |—————————–-------|
CD     |——-AB(2min)————->| ( AB comes and A returns)
ACD   |<——-A-(1min)————--|B
A       || ——-CD(10min)———>| BCD  (CD come and B returns)
A ||    |<——-B-(2min)————--|
AB     |—————————–-------|ABCD  (AB come)
If you count all the trips ie. 2+1+10+2+2, it will be 17 minutes

Question 9:

Why is it very common to have a 9 minute snooze interval on alarm clocks, why not 10 instead? Answer: By setting the snooze time to 9 minutes, the alarm clock only needs to watch the last digit of the time. So, if you hit snooze at 6.45, the alarm goes off again when the last digit equals 4. They couldn't make it 10 minutes, otherwise the alarm would go off right away, or it would take more circuitry.

Question 10:

A bookworm eats from the first page of an encyclopedia to the last page. The bookworm eats in a straight line. The encyclopedia consists of ten 1000-page volumes and is sitting on a bookshelf in the usual order. Not counting covers, title pages, etc., how many pages does the bookworm eat through?
Answer: On a book shelf the first page of the first volume is on the "inside"

__                             __
      B|  |                           |  |F
      A|1 |...........................|10|R
      C|  |                           |  |O
      K|  |                           |  |N
       |  |                           |  |T
       ----------------------------------
 

so the bookworm eats only through the cover of the first volume, then 8 times 1000 pages of Volumes 2 - 9, then through the cover to the 1st page of Vol 10. He eats 8,000 pages.

Question 11:

An Arab sheikh tells his two sons to race their camels to a distant city to see who will inherit his fortune. The one whose camel is slower will win. The brothers, after wandering aimlessly for days, ask a wise man for advise. After hearing the advice they jump on the camels and race as fast as they can to the city. What does the wise man say?
Answer: Solution »

Question 12:

An 18-wheeler is crossing a 4 kilometer bridge that can only support 10,000 kilograms and that's exactly how much the rig weighs. Halfway across the bridge a 30 gram sparrow lands on the cab, but the bridge doesn't collapse. Why not?
Answer: Solution »

Question 13:

A completely black dog was strolling down Main Street during a total blackout affecting the entire town. Not a single streetlight had been on for hours. Just as the dog was crossing the middle line a Buick Skylark with 2 broken headlights speedily approaches his position, but manages to swerve out of the way just in time. How could the driver have possibly seen the dog to swerve in time?
Answer: Solution »

Question 14:

In a small cabin in the woods, two men lay dead. The cabin itself is not burned, but the forest all around is burned to cinders. How did the men die?
Answer: Solution »

Question 15:

Ida puts her coffee into the microwave, as she does every morning, for exactly 2 minutes. When the microwave goes off, she opens the door, but then closes the door again and sets the microwave for 2 more seconds. What good would 2 more seconds be?
Answer: Solution »

Question 16:

Beulah died in the Appalachians while Craig died at sea. Everyone was much happier with Craig's death. Why?
Answer: Solution »

Question 17:

You are a cook in a remote area with no clocks or other way of keeping time other than a four minute sandglass timer and a seven minute sandglass timer. (The kind you turn over - hourglass shaped) You do have a stove, however, with water in a pot already boiling. Somebody asks you for a nine-minute egg, and you know this person is a perfectionist and will be able to tell if you undercook or overcook the eggs by even a few seconds. What is the least amount of time it will take to prepare the egg? And how will you prepare it so that it is neither undercooked or overcooked?
Answer: Solution »

Question 18:

I am the owner of a pet store. If I put in one canary per cage, I have one bird too many. If I put in two canaries per cage, I have one cage too many. How many cages and canaries do I have?
Answer: Solution »

Question 19:

Here is a series of numbers. What is the next number in the sequence?
1
11
21
1211
111221
312211
13112221
Answer: Solution »

Question 20:

My daughter has many sisters. She has as many sisters as she has brothers. Each of her brothers has twice as many sisters as brothers. How many sons and daughters do I have?
Answer: Solution »

Question 21:

What seven-letter word has hundreds of letters in it?
Answer: Solution »

Question 22:

If you had a ton of feathers and a ton of stones which would be heavier?
Answer: Solution »

Question 23:

Tom's mother has three children. One is named April, one is named May. What is the third one named?
Answer: Solution »

Question 24:

Two women apply for a job. They are identical. They have the same mother, father and birthday. The interviewer asks, "Are you twins?" to which they honestly reply, "No".
How is this possible?
Answer: Solution »

Question 25:

You are standing outside a closed door. On the other side of the door is a room that has three light bulbs in it. The room is completely sealed off from the outside. It has no windows and nothing can get in or out except through the door. On the outside of the room there are three light switches that control each of the respective light bulbs on the other side of the door.
                Your assignment is to determine which light switch controls which light bulb. You are allowed to enter the room only once, and once you come out, you must be able to state with 100% certainty which light switch controls which light bulb.
Answer: Solution »

Question 26:

If a bottle and a cork cost a dollar and a nickel, and the bottle costs a dollar more than the cork, how much does the cork cost?
Answer: Solution »

Question 27:

A boat has a ladder that has six rungs. Each rung is one foot apart. The bottom rung is one foot from the water. The tide rises at 12 inches every 15 minutes. High tide peaks in one hour.
         When the tide is at its highest, how many rungs are under water?
Answer: Solution »

Question 28:

You have a lighter and two fuses that take exactly one hour to burn, but they don't burn at a steady rate. For example, one fuse could take 59 minutes to burn the first inch and then burn the rest of the fuse in the last minute.
         How would you use these two fuses to measure 45 minutes?
Answer: Solution »

Question 29:

You have two buckets - one holds exactly 5 gallons and the other 3 gallons. How can you measure 4 gallons of water into the 5 gallon bucket?
(Assume you have an unlimited supply of water and that there are no measurement markings of any kind on the buckets.)
Answer: Solution »

Question 30:

A princess is as old as the prince will be when the princess is twice the age that the prince was when the princess's age was half the sum of their present ages.
What are their ages?
Answer: Solution »

Question 31:

During WWII, there was a bridge connecting Germany and Switzerland, and on the German side, there was a sentry tower with a guard in it. He would come out every three minutes to check on the bridge, and he had orders to turn back anyone who tried to get into Germany, and shoot anyone trying to escape without a pass. There was a woman who desperately needed to get into Switzerland, and she knew she didn't have time to get a pass. It would take her at least six minutes to cross the bridge, but she managed to do it. How?
Answer: Solution »

Question 32:

A man can make perfect counterfeit bills. They look exactly like real ones, they're made of exactly the same materials, made the same way, everything. So perfect, one could pretty much call them real bills. One day he successfully makes a perfect copy of another bill. However, he gets caught when he tries to use the copy. How is this possible?
Answer: Solution »

Question 33:

A prisoner is told "If you tell a lie we will hang you; if you tell the truth we will shoot you." What can he say to save himself?
Answer: Solution »

Question 34:

How many people can read hex if only you and dead people can read hex?
Answer: Solution »

Question 35:

A man is traveling with a fox and two chickens, if he leaves the fox alone with the chickens the fox will eat the chickens. He comes to a river and needs to cross it, he finds a small boat that can carry only him and one animal, how does he get himself, the fox and two chickens across the river safely?
Answer: Solution »

Question 36:

A man is looking at a picture of a man on the wall and states: Brothers and sisters I have none, but this man's father is my father's son. Who is the man in the picture in relation to the man looking at the picture?
Answer: Solution »

Question 37:

A man and his son had a terrible car accident and were rushed to the hospital. The man died on the way, but the son was still alive and a surgeon was called in to operate. However, the surgeon saw the young boy and said, "I can't operate on this boy. He's my son."
How is this possible?
Answer: Solution »

Question 38:

A wise king devised a contest to see who would receive the Princess' hand in marriage. The Princess was put in a 50x50 foot carpeted room. Each of her four suitors were put in one corner of the room with a small box to stand on. The first one to touch the Princess hand would be the winner and become the new King.
The rules of the test were that the contestants could not walk over the carpet, cross the plane of the carpet, or hang from anything; nor could they use anything but their body and wits (i.e. no magic or telepathy, nor any items such as ladders, block and tackles etc). One suitor figured out a way and married the Princess and became the new King. What did he do?
Answer: Solution »

Question 39:

Two guards were on duty outside a barracks. One faced up the road to watch for anyone approaching from the North. The other looked down the road to see if anyone approached from the South. Suddenly one of them said to the other, "Why are you smiling?"
How did he know his companion was smiling?
Answer: Solution »

Question 40:

You're riding a horse. To the right of you is a cliff and in front of you is an elephant going the same pace as you and you can't overtake it. To the left of you is a hippo running at the same speed and behind you is a lion chasing you. How do you get to safety?
Answer: Solution »

Question 41:

You have 50 quarters on the table in front of you. You are blindfolded and cannot discern whether a coin is heads up or tails up by feeling it. You are told that x coins are heads up, where 0 < x < 50. You are asked to separate the coins into two piles in such a way that the number of heads up coins in both piles is the same at the end. You may flip any coin over as many times as you want. How will you do it?
Answer: Solution »

Question 42:

You have four chains. Each chain has three links in it. Although it is difficult to cut the links, you wish to make a single loop with all 12 links. What is the fewest number of cuts you must make to accomplish this task?
Answer: Solution »

Question 43:

Walking down the street one day, I met a woman strolling with her daughter. "What a lovely child," I remarked. "In fact, I have two children," she replied. What is the probability that both of her children are girls?
Answer: Solution »

Question 44:

Three closed boxes have either white marbles, black marbles or both, and they are labeled white, black and both. However, you're told that each of the labels are wrong. You may reach into one of the boxes and pull out only one marble. Which box should you remove a marble from to determine the contents of all three boxes?
Answer: Solution »

Question 45:

A glass of water with a single ice cube sits on a table. When the ice has completely melted, will the level of the water have increased, decreased or remain unchanged?
Answer: Solution »

Question 46:

You are given eight coins and told that one of them is counterfeit. The counterfeit one is slightly heavier than the other seven. Otherwise, the coins look identical. Using a simple balance scale, can you determine which coin is counterfeit using the scale only once?
Answer: Solution »

Question 47:

You are given eight coins and told that one of them is counterfeit. The counterfeit one is slightly heavier than the other seven. Otherwise, the coins look identical. Using a simple balance scale, can you determine which coin is counterfeit using the scale only twice?
Answer: Solution »

Question 48:

I was visiting a friend one evening and remembered that he had three daughters. I asked him how old they were. "The product of their ages is 72," he answered. Quizzically, I asked, "Is there anything else you can tell me?" "Yes," he replied, "the sum of their ages is equal to the number of my house." I stepped outside to see what the house number was. Upon returning inside, I said to my host, "I'm sorry, but I still can't figure out their ages." He responded apologetically, "I'm sorry, I forgot to mention that my oldest daughter likes strawberry shortcake." With this information, I was able to determine all of their ages. How old is each daughter? You have enough information to solve the puzzle.
Answer: Solution »

Question 49:

You're in a room with two doors. There's a guard at each door. One door is the exit, but behind the other door is something that will kill you. You're told that one guard always tells the truth and the other guard always lies. You don't know which guard is which. You are allowed to ask one question to either of the guards to determine which door is the exit. What question should you ask?
Answer: Solution »

Question 50:

How far can a dog run into the forest?
Answer: Solution »

Question 51:

If eggs are 12¢ a dozen, how much would it cost for 100 eggs?
Answer: Solution »

Question 52:

You are a prisoner sentenced to death. The Emperor offers you a chance to live by playing a simple game. He gives you 50 black marbles, 50 white marbles and 2 empty bowls. He then says, "Divide these 100 marbles into these 2 bowls. You can divide them any way you like as long as you use all the marbles. Then I will blindfold you and mix the bowls and marbles up. You can then choose one bowl and remove one marble. If the marble is white, you live, but if the marble is black...you die.
                   How do you divide the marbles up so that you have the greatest probability of choosing a white marble?
Answer: Solution »

Question 53:

What is the next number in this series?
1, 2, 6, 42, 1806, ?
Answer: Solution »

Question 54:

What do the following numerals specify?
11111121113122223222
Answer:  Solution »

Question 55:

You must buy 100 chickens for exactly $100. You must buy at least one chicken from each store. The first store charges 5 cents/chicken, the second charges $1/chicken and the third charges $5/chicken. How many chickens should you buy from each store?
Answer: Solution »

Question 56:

What is special about the following number sequence?
8, 5, 4, 9, 1, 7, 6, 10, 3, 2, 0
Answer: Solution »