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Infosys Logic Interview Question

Infosys Logic Interview Question - 17 June

This was asked in an interview of Infosys.

Interviewer has given me 100 marbles(50 white and 50 black) and two empty boxes.
He then told me that he will leave the room and i need to place all the marbles in two boxes.

And When he come back, he will draw a marble from any of the two box and if the marble is black i will be hired.

Also
* No box can be empty.
* All 100 marbles must be placed in one of the two boxes.

So whats should i have done ?

For Solution : Click Here

22 comments:

  1. in one box add black marble and rest in other box

    ReplyDelete
    Replies
    1. if he took white 4m the other box means wat will u do? :P

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    2. This is about probability if u understand that you would have not asked this question....
      Actually he cannot make sure 100% to take black only, but he can arrange it maximum possibility to take black only if you arrange like this...
      if that man picks up from first (one black marble)100% winning chance, if he picks from other 49/99 chance of getting black.... which could be the maximum probability in this case.

      Delete
  2. adding marbles in such a way that twenty five white marbles on both boxes will stay in bottom and twenty five marbles in top.

    ReplyDelete
  3. put one black marble in one box and rest of 99 marbles in another box, this way if marble is drawn from first box u will be hired, otherwise you still have a chance of 50-50.

    ReplyDelete
  4. Put all 50 white Marbles in one box, Put second box upside down and put 50 black marbles on top of it. This makes him selected for sure as he ensured :

    1. 100 Marbles in one box,
    2. He has kept one box inside another where 1 filed with air and other with marbles.
    3. 100% probability of picking only Black Marble.

    ReplyDelete
    Replies
    1. and if he stucks his hand deep in the box then? wat wil u do? :P

      Delete
  5. IN EACH BOX 25 BLACK MARBLES SHOULD BE KEPT.

    ReplyDelete
  6. he need to find some mild acids in the room then apply them on white marbles, then put them in any ratio in any box. with acid marble turns black, so eventually he will choose only black. (I am not sure of any thing that is available in the room that can act as acid so if you any thing comment it).

    ReplyDelete
    Replies
    1. How stupid are u idiot ?????

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    2. Defenitely you will be hired. Just send your resume to Narayanamurthy :-)

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    3. hahaha..... this one is the most hilarious answer i ever heard.

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    4. unga aaya va kakus kaluvranga acid vechukuradhuku?

      Delete
  7. I would say place 1 black marble in box1;
    put rest in box2

    so your totally chance will incerase as
    chance of box1 getting selcted = 50% so chance of black till now =50%
    chance of box2 getting selected= 50%,
    in which chance of black getting selected is 49/99 = aroun 25%

    so total chance of black selected = 75%
    Is this d right ans ?

    ReplyDelete
  8. place the boxes...one inside the other.....the inner box edges can be first filled with white marbles and over that all the black marbles....edges that too below the black marble layer wont be reached....that way both boxes r filled....n he can reach the black marble first.

    ReplyDelete
  9. u probability morons and acid scientists.... its a simple question.....

    take one box, put all white marbles in it, then take another empty box and place it inside the that box and put black marbles in it. this way all white marbles will remain beneath the upper box containing black marbles..
    so, u can say that the lower box contains 100 marbles
    no box is empty
    and the drawer cant draw white marble in any case. he is drawing marble from the 2 boxes and he will draw only black.

    ReplyDelete
    Replies
    1. To put one box inside the other there has tobe a size difference isnt it? What if both the boxes are of same size and one cannot be put into another???

      Delete
  10. its very simple guys...
    probability of choosing one box over the another is 50%. i hope that is well understood.
    so put one black marble in one box...so if the interviewer chooses that box he is going to find nothing but black.
    and in the remaining put the 49 black marbles with 50 white marbles so the probability of the other box also goes higher to 49%.
    Which means total probability shoots up to 75% of you getting hired.
    That's the answer.

    ReplyDelete
  11. Also
    * No box can be empty.
    * All 100 marbles must be placed in one of the two boxes.

    ===============
    how will both condition exists..
    All 100 marbles must be placed in one of the two boxes in the sense all
    100 marbales should be put in one box...

    ReplyDelete
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    ReplyDelete