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Combinatorics Question?

1) If out of n things p are alike, q are alike, r are alike and s are alike and (n - p - q - r - s = t) are different, then prove that the total no of combinations will be (p + 1)(q + 1)(r + 1)(s + 1)(2^t) - 1

2) If we have to distribute 5 chocolates in 4 people, we know that there are

i) 4^5 ways if the chocolates are distinguishable

ii) C[8,3] ways if they are same.

What if the chocolates are partly identical.

i.e. say out of 5 you have 3 identical. I would like a general formula here not the answer to the question.

3 Answers

Relevance
  • 9 years ago
    Favorite Answer

    1)

    Out of p alike things, we may choose one or more or none. Thus, there are (p+1) ways of choosing none or one or more of p things. If * denotes that none of the p things are chosen, these combinations can be expressed as {*}, {p}, {pp}, {ppp}, ... {ppp upto p things}.

    Similarly, there are (q+1) ways of choosing or not choosing one or more of q alike things and so on.

    For t different things, we have two choices for each of them, choosing or not choosing which means that there are 2^t ways of choosing or not choosing each of t different things.

    Thus, there are (p+1)(q+1)(r+1)(s+1)(2^t) ways of choosing things out of n things which include a possibility of not choosing any. Hence, the total number of ways of choosing excluding a combination in which none is chosen is

    (p+1)(q+1)(r+1)(s+1)(2^t) - 1.

  • ?
    Lv 4
    5 years ago

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  • M3
    Lv 7
    9 years ago

    q2

    2 distinguishable, 3 identical to 4 people

    4^2 ways for distinguishable,

    C(6,3) for identical

    multiply to get ans

    p distinguishable, q identical to r people

    r^p *C(q+r-1,r-1)

    ---------------------

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