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Question Number 125413 by Hassen_Timol last updated on 11/Dec/20

Knowing that :  Σ_(k=0) ^n  ((n),(k) )^2  =  (((2n)),((  n)) )    We have p tokens and n boxes.  Each box is labeled with a number from 1 to n.  Each box is enough big to receive all p tokens.    In how many ways can we share the token :  a)   if we can distinguish all tokens ?  b)   if all the tokens are the same ?    NB : the boxes may have 0,1,2...,p tokens in them.

Knowingthat:nk=0(nk)2=(2nn)Wehaveptokensandnboxes.Eachboxislabeledwithanumberfrom1ton.Eachboxisenoughbigtoreceiveallptokens.Inhowmanywayscanwesharethetoken:a)ifwecandistinguishalltokens?b)ifallthetokensarethesame?NB:theboxesmayhave0,1,2...,ptokensinthem.

Commented by Hassen_Timol last updated on 10/Dec/20

Could you help me please...?

Answered by mr W last updated on 11/Dec/20

a)  n^p     b)  (1+x+x^2 +...)^n =(1/((1−x)^n ))=Σ_(k=0) ^∞ C_k ^(k+n−1) x^k   coefficient of x^p  is C_p ^(p+n−1)

a)npb)(1+x+x2+...)n=1(1x)n=k=0Ckk+n1xkcoefficientofxpisCpp+n1

Commented by Hassen_Timol last updated on 11/Dec/20

Thank you a lot ! I am sorry that I didn't understand but what is x ?

Commented by mr W last updated on 11/Dec/20

i used generating function method.  x is here just a symbol for variable.  we can also solve (b) using stars &  bars method und get C_(n−1) ^(p+n−1)  which  is the same as C_p ^(p+n−1) .

iusedgeneratingfunctionmethod.xisherejustasymbolforvariable.wecanalsosolve(b)usingstars&barsmethodundgetCn1p+n1whichisthesameasCpp+n1.

Commented by Hassen_Timol last updated on 12/Dec/20

Thank you very much

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