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Is n-1 divisible by 3 ?

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by ronaldramlan » Sat Aug 06, 2011 8:16 pm
Given that n is an integer, is n - 1 divisible by 3?

(1) n^2+n is not divisible by 3
(2) 3n+5>=K+8 , where k is a positive multiple of 3

(A) Statement (1) alone is sufficient, but statement (2) alone is not sufficient.
(B) Statement (2) alone is sufficient, but statement (1) alone is not sufficient.
(C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
(D) Each statement ALONE is sufficient.
(E) Statements (1) and (2) TOGETHER are NOT sufficient.

I'll post OA later ...
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Source: — Data Sufficiency |
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by Frankenstein » Sat Aug 06, 2011 9:23 pm
Hi,
From(1):
n(n+1) is not divisible by 3.
So, n and (n+1) are nor divisible by 3.
Whenever you pick 3 consecutive integers, 1 should be a multiple of 3 and the other two not.
As (n-1),n,(n+1) are consecutive and n,(n+1) not divisible by 3, (n-1) should be divisible by 3.
Sufficient

From(2):
Let k = 3, 3n+5 >= 11 =>n>=2
So, n-1 >= 1
This can be either a multiple of 3 or not
Not sufficient

Hence, A
Cheers!

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by ajaykpat » Sun Aug 07, 2011 12:52 am
statement 1 : sufficient

Statement 2 : not sufficient


nice explanation from Frankenstein


IMO: A
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