Third-class 8334

If we add one element to set A, the number of third-class variations increases two times. How many elements did the set initially contain?

Correct answer:

n =  5

Step-by-step explanation:

V(n,3) = n(n1)(n2) 2 V(n,3) = V(n+1,3) 2 n(n1)(n2) = (n+1)n(n1) 2 (n2) = (n+1)  2 (n2)=(n+1)  n=5  n=15=5  n=5   Verifying Solution:   n1=n (n1) (n2)=5 (51) (52)=60 n2=(n+1) (n) (n1)=(5+1) 5 (51)=120  n2=2n1

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