It is currently 20 Jan 2018, 09:05

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Is a divisible by 3?

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Aug 2009
Posts: 5534

Kudos [?]: 6440 [0], given: 122

Is a divisible by 3? [#permalink]

### Show Tags

04 Jan 2018, 08:15
Expert's post
1
This post was
BOOKMARKED
00:00

Difficulty:

75% (hard)

Question Stats:

36% (01:07) correct 64% (00:37) wrong based on 53 sessions

### HideShow timer Statistics

Is $$a$$ divisible by $$3$$?

(1) $$a+3b$$ is divisible by $$3$$.
(2) $$b$$ is divisible by $$3$$.

New Question
[Reveal] Spoiler: OA

_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

BANGALORE/-

Kudos [?]: 6440 [0], given: 122

Manager
Joined: 23 Feb 2017
Posts: 56

Kudos [?]: 40 [0], given: 14

Re: Is a divisible by 3? [#permalink]

### Show Tags

04 Jan 2018, 09:46
Ans A

Statement 1 a+3b is divisible by 3.

3b will be multiple of 3 so as a.

sufficient

Statement 2 b is divisible by 3.
not sufficient
_________________

+1 Kudos if you find it helpful.

Kudos [?]: 40 [0], given: 14

DS Forum Moderator
Joined: 21 Aug 2013
Posts: 671

Kudos [?]: 214 [0], given: 299

Location: India
Re: Is a divisible by 3? [#permalink]

### Show Tags

04 Jan 2018, 10:16
chetan2u wrote:
Is $$a$$ divisible by $$3$$?

(1) $$a+3b$$ is divisible by $$3$$.
(2) $$b$$ is divisible by $$3$$.

New Question

Here we are NOT given that a/b are integers, so we cannot assume them to be so.

(1) a+3b is divisible by 3. If b =2/3, this makes 3b = 2. Now we can have a = 1, which makes a+3b divisible by 3, and here 'a' is NOT divisible by 3.
But we can have another case say b = 1, here 3b = 3. Now whichever value a takes will have to be a multiple of 3 (eg, 3, 6,..) in order for a+3b to be a multiple of 3.
So 'a' can or cannot be a multiple of 3. Not sufficient.

(2) This doesnt tell anything about 'a', so definitely Not Sufficient.

Combining the two statements, since b is divisible by 3, b has to be an integer. So 3b will also definitely be an integer. Now a+3b is also divisible by 3 and 3b is divisible by 3..this can only happen if 'a' too is divisible by 3. Sufficient.

Kudos [?]: 214 [0], given: 299

VP
Status: Learning
Joined: 20 Dec 2015
Posts: 1106

Kudos [?]: 104 [0], given: 607

Location: India
Concentration: Operations, Marketing
GMAT 1: 670 Q48 V36
GRE 1: 314 Q157 V157
GPA: 3.4
WE: Manufacturing and Production (Manufacturing)
Re: Is a divisible by 3? [#permalink]

### Show Tags

04 Jan 2018, 22:18
chetan2u wrote:
Is $$a$$ divisible by $$3$$?

(1) $$a+3b$$ is divisible by $$3$$.
(2) $$b$$ is divisible by $$3$$.

New Question

Hi Can any body explain the error in my solution please.
Statement 1
a+3b is divisible by 3 that means a+3b=3x where x is some number
now a=3x-3b
a=3*(x-b) thus it is divisible by 3 hence sufficient .
_________________

We are more often frightened than hurt; and we suffer more from imagination than from reality

Kudos [?]: 104 [0], given: 607

SVP
Joined: 12 Dec 2016
Posts: 1860

Kudos [?]: 181 [0], given: 2406

Location: United States
GMAT 1: 700 Q49 V33
GPA: 3.64
Is a divisible by 3? [#permalink]

### Show Tags

04 Jan 2018, 22:48
arvind910619 wrote:
chetan2u wrote:
Is $$a$$ divisible by $$3$$?

(1) $$a+3b$$ is divisible by $$3$$.
(2) $$b$$ is divisible by $$3$$.

New Question

Hi Can any body explain the error in my solution please.
Statement 1
a+3b is divisible by 3 that means a+3b=3x where x is some number
now a=3x-3b
a=3*(x-b) thus it is divisible by 3 hence sufficient .

it is because a or b can still be non-integer numbers.

===============
kudos if you find my post helpful. Thanks

Kudos [?]: 181 [0], given: 2406

Is a divisible by 3?   [#permalink] 04 Jan 2018, 22:48
Display posts from previous: Sort by