If the number of elements is decreased by two, the number of permutations is decreased 30 times. How many elements are?

Correct answer:

n =  6

Step-by-step explanation:

P(n)=n! P(n) = 30 P(n2) n! = 30 (n2)! n(n1)(n2)! = 30 (n2)! n(n1)=30  n2n30=0  a=1;b=1;c=30 D=b24ac=1241(30)=121 D>0  n1,2=2ab±D=21±121 n1,2=21±11 n1,2=0.5±5.5 n1=6 n2=5  n=n1=6

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