# QUESTION 1: The “odd/even factorial” of a positive integer n is represented as n!! and is defined non-recursively as: (n)(n-2)(n-4)…(4)(2) if n is even and is (n)(n-2)(n-4)…(5)(3) (1) if n is odd. What are the respective values of 6!! and 9!! ? A) 48 and 945 B) 24 and 315 C) 48 and 909 D) 24 and 303 E) 24 and 909 QUESTION 2: Which is a valid recursive definition of n!!? A) (n)(n-2)(n-4)(n-6)(n-8)…(n-(n-2)) B) n*(n-2)!! C) n when n is less than 3, n*(n-2)!! otherwise D) none of the above

### CHALLENGE:

QUESTION 1:

The “odd/even factorial” of a positive integer n is represented as n!! and is defined non-recursively as: (n)(n-2)(n-4)…(4)(2) if n is even and is (n)(n-2)(n-4)…(5)(3) (1) if n is odd. What are the respective values of 6!! and 9!! ?

A) 48 and 945
B) 24 and 315
C) 48 and 909
D) 24 and 303
E) 24 and 909

QUESTION 2:

Which is a valid recursive definition of n!!?

A) (n)(n-2)(n-4)(n-6)(n-8)…(n-(n-2))
B) n*(n-2)!!
C) n when n is less than 3, n*(n-2)!! otherwise
D) none of the above

### SOLUTION:

```Q1-48 and 945

Q2-n when n is less than 3, n*(n-2)!! Otherwise
```