Question 1147295
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I don't see how it makes any sense to ask to show work in factorial notation....<br>
{{{nP4 = n(n-1)(n-2)(n-3)}}}<br>
{{{nC2 = (n(n-1))/2}}}<br>
So<br>
{{{n(n-1)(n-2)(n-3) = 84((n(n-1))/2)}}}
{{{(n-2)(n-3)=42}}}<br>
(n-2) and (n-3) are consecutive positive integers; their product is 42.  You should be able to solve that equation by inspection....<br>