a firm has 23 senior and 24 junior partners. a committee of three partners is selected at random to represent the firm at a conference. in how many ways can at least one of the junior partners be chosen to be on the committee?

Respuesta :

Total number of selecting three partners randomly in which at least one junior partner must be there out of 23 senior and 24 junior partners is 14,444

                     

Combination:

                       Combination is the number of possible ways, where order is irrelevant and replacements are not permitted, to select a sample of r elements from a set of n different objects.

                             [tex]C(n,r)=nCr = \frac{n!}{(n-r)! r!}[/tex]

  C(n, r) means, Selection of r things out of n different things

           According to question,

        Given,

                    A firm has 23 senior and 24 junior partners.

      We have to select three partners randomly in which at least one junior partner must be there.

Case I : 2 senior and 1 junior partners

            2 senior partners can be selected out of 23 in C(23,2) ways

            1 junior partner can be selected out of 24 in C(24,1) ways

      hence number of ways of selecting 2 senior and 1 junior partners is equal to

                      C(23,2) x C(24,1)

Case II :  2 senior and 1 junior partners

               1 senior partners can be selected out of 23 in C(23,1) ways

               2 junior partner can be selected out of 24 in C(24,2) ways

      hence number of ways of selecting 1 senior and 2 junior partners is equal to

                          C(23,1) x  C(24,2)    

Case III :  0 senior and 3 junior partners

               0 senior partners can be selected out of 23 in C(23,0) ways

               3 junior partner can be selected out of 24 in C(24,3) ways

      hence number of ways of selecting no senior and 3 junior partners is equal to

                          C(23,0) x  C(24,3)    

Thus,

        Total number of selecting three partners randomly in which at least one junior partner must be there is

             

           C(23,2) x C(24,1) +  C(23,1) x  C(24,2)   + C(23,0) x  C(24,3)  

Using formula,

                           [tex]C(n,r)=nCr = \frac{n!}{(n-r)! r!}[/tex]

       C(23,2) x C(24,1) +  C(23,1) x  C(24,2)   + C(23,0) x  C(24,3)  

    =    253    x 24        +  23        x  276        + 1           x 2024

    =    6072   +  6348 + 2024

    =    14,444

Total number of selecting three partners randomly in which at least one junior partner must be there is 14,444

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