sjuniv32 wrote:
If n is a positive integer, then n (n+1) (n+2) is which of the following?
(A) even only when n is even
(B) even only when n is odd
(C) odd whenever n is odd
(D) divisible by 3 only when n is odd
(E) divisible by 12 whenever n is even
Source: Veritas Prep, Book- Arithmetic, Third edition, Page-260
Here, n, (n+1), and (n+2) are 3 consecutive integers
The product of 3 consecutive positive integers is always divisible by 3!
Note: The product of k consecutive positive integers is always divisible by k!Example:
The product of 2 consecutive positive integers is always divisible by 2!
The product of 3 consecutive positive integers is always divisible by 3!
The product of 4 consecutive positive integers is always divisible by 4! and so on
Why? Considering positive integers:
# When we have 2 consecutive integers, one will be even and the other odd => Their product is even - divisible by 2 = 2!
# When we have 3 consecutive integers, one number will always be a multiple of 3. Also, 3 consecutive integers will include 2 consecutive integers.Thus, the product will be divisible by 2 x 3 => Their product is divisible by 6 = 3!
# When we have 4 consecutive integers, one number will always be a multiple of 4. Also, 4 consecutive integers will include 3 consecutive integers.Thus, the product will be divisible by 3! x 4 => Their product is divisible by 4!
In the above question:
n(n + 1)(n + 2) must be divisible by 3! = 6 (since one number must be a multiple of 3 and at least one number is even)
Thus, n(n + 1)(n + 2) is always even and always a multiple of 3
Thus, Options A, B, C, and D are incorrect.
Now, if n is even, (n + 2) is also even
Thus, n(n + 1)(n + 2) must be divisible by 3 x 2 x 2 = 12
Answer E