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  n(n1)=30 n2n30=0  a=1;b=1;c=30 D=b24ac=1241(30)=121 D>0  n1,2=b±D2a=1±1212 n1,2=1±112 n1,2=0.5±5.5 n1=6 n2=5   Factored form of the equation:  (n6)(n+5)=0  n=n1=6=6

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