Monday, May 7, 2012

Secret box

There is a box with 20 red balls, 10 green balls and 5 black balls. How many balls do we have to extract at least to get four balls with the same colour?

CLUE: Think about the worst possible situation.

Use comments to answer, writing your name.


(Translated from: 100 problemas de ingenio by Capó, M.)

17 comments:

  1. Mª Jesús Grueso Alcántara 1º ESO BMay 7, 2012 at 10:07 PM

    I think that it's 10 balls.

    ReplyDelete
  2. Remedios Ros GraciaMay 8, 2012 at 4:33 PM

    I'm not sure, but I think we have to extract 10 balls.

    ReplyDelete
  3. guillermo valverde maestrMay 9, 2012 at 4:15 PM

    We have to extract 29 balls

    ReplyDelete
  4. Marina Varas Santolalla 1ºESO B
    Para sacar 4 bolas del mismo color hay que sacar al menos 17 bolas

    ReplyDelete
  5. We have to extract 6 balls.

    Julia Rodríguez Pedrera 1ºESO B

    ReplyDelete
  6. SOLUCION:10 BALLS

    ReplyDelete
  7. Como mínimo, son 4 las que se necesitan, aunque hay una probabilidad pequeña de que salgan las 4 primeras del mismo color.




    Jesús Mejías Cabello de Alba 1ºB

    ReplyDelete
  8. If you take 4 balls you have posibilities to get all with the same color, so, 4 is the minimun
    Ana Sevilla Moreno 1ºESO B

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  9. Miguel Limonchi PedrazaMay 10, 2012 at 9:20 PM

    la peor opcion es sacar diez bolas y tendriamos cuatro bolas de un mismo color necesariamente

    ReplyDelete
  10. CARLOS GRACIA MARMOL 1 ESO BMay 10, 2012 at 9:34 PM

    Is to take 10 balls at a minimum.
    Carlos Gracia Mármol 1 ESO B

    ReplyDelete
  11. Ana Juárez Moreno 1º Eso BMay 10, 2012 at 9:54 PM

    10

    ReplyDelete
  12. Javier Anglada. 1º ESO B
    The answer is ten balls.
    The smaller number of balls you can extract without having four with the same colour is nine (3+3+3). If you extract another ball, regardless of colour, you will have four equal balls.

    ReplyDelete
  13. mari angeles ruz
    profesor me ha costado mucho trabajo y no se si esta bien...
    SOLUCION: hacen falta sacar 28 bolas

    ReplyDelete
  14. Hay que extraer 17 bolas para conseguir 4 del mismo color.

    Noelia González Oteros 1ºB

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  15. Marina Varas Santolalla
    Cambio mi respuesta enviada a: Hay que sacar como minimo 10 bolas.

    ReplyDelete
  16. I change my answer you have to take 12 because the worse situation is that you do not take any balls at the same color so is 4 times 3.
    Ana Sevilla Moreno 1ºESO B

    ReplyDelete
  17. The right answer is 10 balls, if you want to know why, read Javier's comment.

    Congratulations!!

    ReplyDelete