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Math Help - combination

  1. #1
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    combination

    there are 24 balls of 6 different sizes in a bag there being 4 balls of each size in four different colours in how many ways 4 balls can be selected so that they are of different colours
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  2. #2
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    Hello, prasum!

    This one is very easy.
    Exactly where is your difficulty?


    \text{There are 24 balls of 6 different sizes in a bag, there being 4 balls of each}
    \text{size in four different colours. \:In how many ways 4 balls can be selected }
    \text{so that they are of different colours?}

    Perhaps the idea of six sizes confused you.
    This was only to show that the six red balls are distinguishable.
    . . They could have been simply numbered: . R_1,\:R_2,\:R_3,\:R_4,\:R_5,\:R_6

    There are 6 choices for a red ball.
    There are 6 choices for a yellow ball.
    There are 6 choices for a blue ball.
    There are 6 choices for a green ball.

    Therefore, there are: . 6^4 = 1296 ways.
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