• Brain Teasers & Puzzles

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    • Here is snippet of section A of the curious multiple-choice entrance exam into the exclusive Puzzlefry puzzle club.


      1. The first question with B as the correct answer is:

      A. 1
      B. 4
      C. 3
      D. 2

      2. The answer to Question 4 is:

      A. D
      B. A
      C. B
      D. C

      3. The answer to Question 1 is:

      A. D
      B. C
      C. B
      D. A

      4. The number of questions which have D as the correct answer is:

      A. 3
      B. 2
      C. 1
      D. 0

      5. The number of questions which have B as the correct answer is:
      A. 0
      B. 2
      C. 3
      D. 1


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    • After the recent Puzzle  annual marathon, the judges were comparing notes to determine who finished where. From their notes, can you help them to reconstruct the final result?

      • Matthew Merryman beat Tom Trent and Jimmy James.
      • Peter Piper beat Jimmy James, Tom Trent and Alan Ardman.
      • Zach Zebra lost to Peter Piper.
      • Graham Goodfellow beat Tom Trent
      • Zach Zebra beat Frank Flintbone.
      • Graham Goodfellow lost to Frank Flintbone and Peter Piper.
      • Tom Trent beat Brian Brick.
      • Alan Ardman beat Zach Zebra, Kevin Kingfisher and Graham Goodfellow.
      • Kevin Kingfisher lost to Graham Goodfellow and Matthew Merryman.
      • Brian Brick beat Kevin Kingfisher.
      • Matthew Merryman lost to Alan Ardman and Zach Zebra.
      • Frank Flintbone beat Tom Trent, Matthew Merryman and Brian Brick.
      • Tom Trent lost to Jimmy James and Alan Ardman.
      • Jimmy James beat Graham Goodfellow and Brian Brick.
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    • At the recent spring fete, four keen gardeners were displaying their fine roses.

      In total there were four colours and each rose appeared in two colours.

      From the clues below can you tell who had which colour roses?

      • Mr Green had a yellow rose.
      • Mr Yellow did not have a red one.
      • Mr Red had a blue rose but not a green one.
      • Mr Blue did not have a yellow one.
      • One person with a red rose also had a green one.
      • One person with a yellow rose also had a blue one.
      • One of the persons with a green rose had no red.
      • Neither of the persons with a yellow rose had a green one.
      • No person has two roses of the same colour.
      • No two persons had the same two colour roses and their names provide no clues.
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    • A king wants an advisor and comes to ask the 3 wisest sages.

      He blindfolds them and put the hats on their head. Afterwards, the king takes off their blindfolds. He tells them that their hat is either blue or white. He tells them that whoever can deduce the color of their hat will be his next advisor. Also he tells them that at least one of the sages will be wearing a blue hat. The sages can all see each other’s hats except of course, their own. Sage A sees that the other 2 are wearing blue hats.
      For hours no one spoke, then Sage A stands up and tells the  king the colour of his hat. What color is it and how does he know?

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      • 4 answers
      • 1 votes

    • King Akbar asked Birbal

      Write something on this wall, which if read in good times, makes you sad and if read in your bad time, makes you happy.

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      • 2 answers
      • 1 votes

    • This was the second problem for Google Code Jam Qualification round 2014, if you are able to solve this problem with the first one(which is very easy) you will be eligible for the next round.


      In this problem, you start with 0 cookies. You gain cookies at a rate of 2 cookies per second, by clicking on a giant cookie. Any time you have at least C cookies, you can buy a cookie farm. Every time you buy a cookie farm, it costs you C cookies and gives you an extra F cookies per second.

      Once you have X cookies that you haven’t spent on farms, you win! Figure out how long it will take you to win if you use the best possible strategy.


      Suppose C=500.0, F=4.0 and X=2000.0. Here’s how the best possible strategy plays out:

        1. You start with 0 cookies, but producing 2 cookies per second.


        1. After 250 seconds, you will have C=500 cookies and can buy a farm that producesF=4 cookies per second.


        1. After buying the farm, you have 0 cookies, and your total cookie production is 6 cookies per second.


        1. The next farm will cost 500 cookies, which you can buy after about 83.3333333seconds.


        1. After buying your second farm, you have 0 cookies, and your total cookie production is 10 cookies per second.


        1. Another farm will cost 500 cookies, which you can buy after 50 seconds.


        1. After buying your third farm, you have 0 cookies, and your total cookie production is 14 cookies per second.


        1. Another farm would cost 500 cookies, but it actually makes sense not to buy it: instead you can just wait until you have X=2000 cookies, which takes about142.8571429 seconds.


      Total time: 250 + 83.3333333 + 50 + 142.8571429 = 526.1904762 seconds.

      Notice that you get cookies continuously: so 0.1 seconds after the game starts you’ll have 0.2 cookies, and π seconds after the game starts you’ll have 2π cookies.


      The first line of the input gives the number of test cases, TT lines follow. Each line contains three space-separated real-valued numbers: CF and X, whose meanings are described earlier in the problem statement.

      CF and X will each consist of at least 1 digit followed by 1 decimal point followed by from 1 to 5 digits. There will be no leading zeroes.


      For each test case, output one line containing “Case #x: y”, where x is the test case number (starting from 1) and y is the minimum number of seconds it takes before you can have X delicious cookies.

      We recommend outputting y to 7 decimal places, but it is not required. y will be considered correct if it is close enough to the correct number: within an absolute or relative error of 10-6. See the FAQ for an explanation of what that means, and what formats of real numbers we accept.


      1 ≤ T ≤ 100.

      Small dataset

      1 ≤ C ≤ 500.
      1 ≤ F ≤ 4.
      1 ≤ X ≤ 2000.

      Large dataset

      1 ≤ C ≤ 10000.
      1 ≤ F ≤ 100.
      1 ≤ X ≤ 100000.



      Input Output
      30.0 1.0 2.0
      30.0 2.0 100.0
      30.50000 3.14159 1999.19990
      500.0 4.0 2000.0


      Case #1: 1.0000000
      Case #2: 39.1666667
      Case #3: 63.9680013
      Case #4: 526.1904762



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    • You are trying to cook an egg for exactly fifteen minutes, but instead of a timer, you are given two ropes which burn for exactly 1 hour each. The ropes, however, are of uneven densities – i e , half the rope length-wise might take only two minutes to burn. How can you cook the egg for exactly fifteen minutes?

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    • On Bagshot Island, there is an airport. The airport is the homebase of an unlimited number of identical airplanes. Each airplane has a fuel capacity to allow it to fly exactly 1/2 way around the world, along a great circle. The planes have the ability to refuel in flight without loss of speed or spillage of fuel. Though the fuel is unlimited, the island is the only source of fuel.
      What is the fewest number of aircraft necessary to get one plane all the way around the world assuming that all of the aircraft must return safely to the airport? How did you get to your answer?

      (a) Each airplane must depart and return to the same airport, and that is the only airport they can land and refuel on ground.
      (b) Each airplane must have enough fuel to return to airport.
      (c) The time and fuel consumption of refueling can be ignored. (so we can also assume that one airplane can refuel more than one airplanes in air at the same time.)
      (d) The amount of fuel airplanes carrying can be zero as long as the other airplane is refueling these airplanes. What is the fewest number of airplanes and number of tanks of fuel needed to accomplish this work? (we only need airplane to go around the world)

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      • 3 answers
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    • You are the ruler of a medieval empire and you are about to have a celebration tomorrow. The celebration is the most important party you have ever hosted. You’ve got 1000 bottles of wine you were planning to open for the celebration, but you find out that one of them is poisoned.

      The poison exhibits no symptoms until death. Death occurs within ten to twenty hours after consuming even the minutest amount of poison.

      You have over a thousand slaves at your disposal and just under 24 hours to determine which single bottle is poisoned.

      You have a handful of prisoners about to be executed, and it would mar your celebration to have anyone else killed.

      What is the smallest number of prisoners you must have to drink from the bottles to be absolutely sure to find the poisoned bottle within 24 hours?

      king and poisioned wine puzzle

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      • 3 answers
      • 1 votes

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