Question 960531


P(a, b) is also written in the form of aPb = a! / (a - b)!

Here we have nP4 = 3(nP3)

n! / (n - 4)! = 3 * n! / (n - 3)!

cancelling n! we have :

1 / (n - 4)! = 3  / (n - 3)!

in fact (n - 3)! is (n - 3) * (n - 3 - 1) * (n - 3 - 2)! = (n - 3)(n - 4)(n - 5)! =  ...

=> we expand it to get the same term we have on the right side :

1 / (n - 4)! = 3  / [(n - 3) * (n - 4)!]

cancelling (x - 4)! we have :

1/1 = 3/(n - 3)

n - 3 = 3

n = 6
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