Question 1083797
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<pre>
n P 3 = n*(n-1)*(n-2).


n C 4 = {{{(n*(n-1)*(n-2)*(n-3))/(1*2*3*4)}}}.


So, your equation is 


n*(n-1)*(n-2) = {{{2*(n*(n-1)*(n-2)*(n-3))/(1*2*3*4)}}}.


Simplify (by canceling the factors n*(n-1)*(n-2) in both sides)


1 = {{{2*((n-3)/24)}}},   or


{{{24/2}}} = n-3  --->  n-3 = 12  --->  n = 15.
</pre>

<U>Answer</U>.  n = 15.