Question 1098386
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In the design of a certain mechanical product, ten components are to be stacked into a cylindrical casing, in a manner 
that minimizes the impact of shocks. One end of the casing is designated as the top and the other end is the bottom.


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a.  If all components are different, how many different stacks are possible?

    10! = 10*9*8*7*6*5*4*3*2*1 = 3628800  different stacks.



b.  If six components are identical to one another, but the others are different, how many different stacks are possible?

    {{{10!/6!}}} = 10*9*8*7 = 5040  different stacks.


c.  If four components are of one type and identical to one another, and four components are of another type 
    and identical to one another, but the others are different, how many different designs are possible?

    {{{10!/(4!*4!)}}} = 6300  different stacks.
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