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25 selected brain teasers

mostly classics

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25 selected brain teasers

  1. 1. 25 selected Brain Teasers Compiled by SRG Oct 2008
  2. 2. Dots and balls 1. Connect nine dots using 4 straight lines without lifting the pencil . . . . . . . . . 2. A factory has 10 machines producing iron balls. All machines produce balls which are identical in appearance but one produces balls weighing 99 gms instead of 100 gms which is the standard. Identify the defective machine with one weighing
  3. 3. 3-6 <ul><li>5. Cryptogram (no leading zeroes) </li></ul><ul><li>MICO + </li></ul><ul><li>PLUG = </li></ul><ul><li>_______ </li></ul><ul><li>GOOD </li></ul><ul><li>6. Six glasses in a row - first three full and last three empty. Moving only one glass make the 1 st , 3 rd and 5 th full and 2, 4 and 6 empty. </li></ul>3. Identify the first letter of this 4 letter word_ E N Y 4. Find the next item in the series: OTTFFSS
  4. 4. 7-8 <ul><li>8. </li></ul><ul><li>Cut a 16X9 carpet into 2 pieces so that the 2 pieces exactly fit the floor of a 12X12 room </li></ul>7 With 6 matchsticks construct 4 equilateral triangles, each with its side equal to the length of the matchstick
  5. 5. 9. Liars <ul><li>“ I am not over 40” says Lata. </li></ul><ul><li>“ Nonsense - you are at least 5 years older than me” says Vandana, “and I am thirty eight” </li></ul><ul><li>“ Ha ha… You are at least 39” says Lata </li></ul><ul><li>All the above statements are untrue </li></ul><ul><li>What are their ages? </li></ul>
  6. 6. 10. Balls again <ul><li>Out of 12 balls that have an identical appearance, 11 have the same weight. However one is either lighter or heavier than the rest. With three weighings using a common balance (no weights) identify the odd one and also whether it is lighter or heavier: </li></ul><ul><li>Variation - use pre-determined weighings </li></ul>
  7. 7. 11-14 Eggs to Gold 11.You have six eggs in a basket. How do you distribute them to six people so that one egg remains in the basket? 12.In a perfect sphere of cheese a hole of uniform diameter is drilled thru the centre. What is the quantity of cheese remaining? 14. Man weighing 90 Kgs has to take 3 gold balls of 5 Kgs in a boat that can take only 100 Kg. How? 13. Using 4 weights you have to measure any weight from 1 to 40. what weights will you choose?
  8. 8. 15. The smartest one <ul><li>Three candidates are being interviewed for a job and have done equally well so far. For the final test, the employer shows a basket with 3 black and one white hat. He blindfolds the candidates and places a hat on each one’s head so that each can see only the hats on the others’ heads. Job goes to the first candidate to rightly identify the color of the hat in the basket. All is quite for a while, then one candidate gives the right answer </li></ul><ul><li>What was the color of the hat in the basket? </li></ul>
  9. 9. 16. Racing King <ul><li>A king was very fond of sponsoring horse races. One day, he sponsored a race where the owner of the last (slowest) horse got the prize for the first place, the owner of the horse that came second from last got the second place and so on. This scheme was publicly announced before the race so that racegoers, the horseowners and the jockeys all knew of this. How does the king ensure that the horses run their fastest, even though the fastest horses don’t get any prizes. </li></ul>
  10. 10. 17. Pilgrim <ul><li>A pilgrim is confronted by 2 gates, each of which is guarded by a sentry. One dorr leads to heaven and the other to hell. One sentry always speaks the truth and the other always lies. The sentries only answer questions with Yes or No and frequently change the doors that they are guarding. The pilgrims does not know which sentry lies and who is truthful. What is the one question that he can ask to either of the sentries that will get him to heaven? </li></ul>
  11. 11. 18.Color of the bear <ul><li>A naturalist starts at point A, walks 1 km south, then 1 km west, where he spots a bear, then goes 1 km north and ends up in point A. What color was the bear? </li></ul>
  12. 12. 19.Violinist <ul><li>A census enumerator visits the math prof’s house and asks him how many kids he has and their ages. “I have three daughters ”, says the prof, “the product of whose ages is 36 and the sum is the same as our house number”. The census taker thinks for a while and then says - “I need one more clue.”. “My eldest daughter plays the violin” says the professor. </li></ul><ul><li>What are the ages of the children? </li></ul>
  13. 13. 20. Salesman <ul><li>The travelling salesman runs out of funds and wires HQ for funds. Knowing, however, that the money may take up to 7 days to reach, he approaches the owner of the inn where he is staying and offers to pay using his gold chain which has seven links at 1 link per day. The inn-keeper agrees, but on condition that he is paid in advance. The salesman is willing to pay on a day to day basis and not for all the 7 days in advance. The owner insists that only one of the 7 links can be cut. How does the salesman pay on a day to basis. The chain looks like this at start. </li></ul>
  14. 14. 21. Five chains <ul><li>I have five chains of 3 links each. </li></ul><ul><li>I request a blacksmith to make one long chain from them. He charges Re 1 for each cut and Re 1 for each weld. What will be my minimum cost? It is lower than Rs 12 </li></ul>
  15. 15. 22. Choice <ul><li>The king asks the princess to choose between two princes Ravan and Duryodhan by making a declaration. If her declaration is true she will marry Ravan who is an evil but truthful man. If her declaration is false, she will marry Duryodhan who is a strong man but a liar. The princess does not want to marry either. How does she escape her fate? </li></ul>
  16. 16. 23-24 23. Cryptogram: TWO + THREE + SEVEN= ______ TWELVE (No leading Zeros) 24. An emperor was born in 36 BC and lived for 100 years. How old was he on his birthday in 38AD?
  17. 17. 25. Cyclists and Bee <ul><li>Two cyclists are travelling towards each other on a road. One is cycling at 7 Kms per hour and the other at 5 Kms per hour. When they are 6 Kms apart, a bee, flying at 8 Kms per hour lands the nose of one cyclist and flies back and forth between the two cyclists till they meet. What is the distance travelled by the bee? </li></ul>
  18. 18. Answers 1-25 <ul><li>1. Diagonal from top right to bottom left. Bottom left to top left, but go higher. Connect middle top and right middle. Go further and turn left to connect bottom right and bottom middle. </li></ul><ul><li>2. Take one from first machine, 2 from second machine and so on </li></ul><ul><li>3 DENY ; 4 One, Two, Three, Four, Five, Six, Seven, Eight </li></ul><ul><li>5 3805+ 2746=6551 (many others possible) </li></ul><ul><li>6 Pour juice from second glass to fourth glass; 7 Pyramid </li></ul><ul><li>8 With 15 as vertical and 9 as horizontal, cut 3 feet horizontally at the 4 th foot from top, then cut 4 ft down, then 3 feet right and so on. </li></ul><ul><li>9 37 and 41 </li></ul><ul><li>10 1,2,3,4 Vs 5,6,7,8; then 1,2,9,5 Vs 4, 10, 11, 8; then 1, 7, 5, 10 vs 12, 11, 2 and 6. Other methods possible. Trick is to two or three weights from one scale to other and analyse result </li></ul><ul><li>11 Sixth guy gets the basket too; 12. A sphere of 10 cms dia. - Hint – assume hole of 0 cms </li></ul><ul><li>13 1, 3, 9, 27; 14. Juggles </li></ul><ul><li>15 White. If anyone had seen the only white, he would have known that the one in the basket is black. Since all kept quite, they all saw black, so the one in the basket is white. </li></ul><ul><li>16 The shuffles the jockeys, so that they ride some other owners’ horse </li></ul><ul><li>17 If I were to ask the other guard to point the door to hell, would he point to this door? </li></ul><ul><li>18 White. This can only happen in the pole, so polar bear. </li></ul><ul><li>19 4, 3, 3 and 6, 6, 1 are the only 2 possible combinations which add up to the same number – 13. So the answer is 4 </li></ul><ul><li>20 Cut the third link to get 1, 2links and 4links. Pay 1 the first day. On second day, pay 2 and get 1 back. And so on. </li></ul><ul><li>21 9;cut one of the 3 chains and use the link to attach other four </li></ul><ul><li>22 “I will marry Duryodhan”; 23 106+ 19722+82524 = 102352 </li></ul><ul><li>24. 73 (no year zero). 25. 4. The bee flies for 30 mins </li></ul>