Question 1179318
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    nP4     =  n*(n-1)*(n-2)*(n-3).


    (n-1)P2 =  (n-1)*(n-2).


Therefore, your equation is


    n*(n-1)*(n-2)*(n-3) = 28(n-1)*(n-2),   assuming  n >= 4.


Cancel the factors  (n-1)  and  (n-2)  in both sides


    n*(n-3) = 28.


You can solve it formally as a quadratic equation, or can guess the solution mentally in two seconds:  n = 7.


<U>ANSWER</U>.   n = 7.
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Solved.