GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 11 Dec 2018, 17:39

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
  • Free GMAT Prep Hour

     December 11, 2018

     December 11, 2018

     09:00 PM EST

     10:00 PM EST

    Strategies and techniques for approaching featured GMAT topics. December 11 at 9 PM EST.
  • The winning strategy for 700+ on the GMAT

     December 13, 2018

     December 13, 2018

     08:00 AM PST

     09:00 AM PST

    What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.

Is a divisible by 3?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7099
Is a divisible by 3?  [#permalink]

Show Tags

New post 04 Jan 2018, 08:15
3
6
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

38% (01:21) correct 62% (00:52) wrong based on 167 sessions

HideShow timer Statistics

Is \(a\) divisible by \(3\)?

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

New Question
Source-self

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


GMAT online Tutor

Manager
Manager
avatar
G
Joined: 23 Feb 2017
Posts: 59
GMAT ToolKit User Premium Member Reviews Badge
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 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.
we don't know about a
not sufficient
_________________

+1 Kudos if you find it helpful.

DS Forum Moderator
avatar
P
Joined: 21 Aug 2013
Posts: 1412
Location: India
Premium Member
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 04 Jan 2018, 10:16
2
2
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.

Hence C answer
VP
VP
User avatar
D
Status: Learning
Joined: 20 Dec 2015
Posts: 1067
Location: India
Concentration: Operations, Marketing
GMAT 1: 670 Q48 V36
GRE 1: Q157 V157
GPA: 3.4
WE: Engineering (Manufacturing)
Reviews Badge CAT Tests
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 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 .
_________________

Please give kudos if you found my answers useful

SVP
SVP
avatar
P
Joined: 12 Dec 2016
Posts: 1652
Location: United States
GMAT 1: 700 Q49 V33
GPA: 3.64
GMAT ToolKit User Premium Member
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 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
Senior Manager
Senior Manager
avatar
G
Joined: 02 Apr 2014
Posts: 474
GMAT 1: 700 Q50 V34
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 22 Jan 2018, 21:56
Good tricky question this.

Statement 1:
if b integer, a + 3b is divisble by 3 => a is divisible by 3
but if b = 1/3, say a = 2, then 2 + 3(1/3) = 3 is divisible by 3, but a = 2 not divisible by 3.

InSuff

Statement 2: clearly insuff

from (1)+(2) , b is not integer, so a has to multiple of 3 => (C)
Intern
Intern
avatar
Joined: 25 Jan 2018
Posts: 4
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 27 Jan 2018, 15:17
Why does “B is divisible by 3” necessarily mean that B is an integer? B could be 3.9 and be divisible by 3. It would yield 1.3. Wouldn’t that be correct?

Posted from my mobile device
PS Forum Moderator
avatar
D
Joined: 25 Feb 2013
Posts: 1217
Location: India
GPA: 3.82
GMAT ToolKit User Premium Member Reviews Badge
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 27 Jan 2018, 19:18
Rurugu wrote:
Why does “B is divisible by 3” necessarily mean that B is an integer? B could be 3.9 and be divisible by 3. It would yield 1.3. Wouldn’t that be correct?

Posted from my mobile device


Hi Rurugu

you get a decimal number only when that integer is not divisible by another integer. For eg. if you divide 5 by 2 then you will get 2.5. 5 when divided by 2 leaves 1 as remainder and that remainder is converted into decimal form.

In your example 3.9=39/10 which will not be divisible by 3.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51100
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 27 Jan 2018, 23:10
Rurugu wrote:
Why does “B is divisible by 3” necessarily mean that B is an integer? B could be 3.9 and be divisible by 3. It would yield 1.3. Wouldn’t that be correct?

Posted from my mobile device


On GMAT when we are told that \(a\) is divisible by \(b\) (or which is the same: "\(a\) is multiple of \(b\)", or "\(b\) is a factor of \(a\)"), we can say that:
1. \(a\) is an integer;
2. \(b\) is an integer;
3. \(\frac{a}{b}=integer\).

Though, still a and b being (positive) integers still would be mentioned.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Intern
Intern
avatar
Joined: 17 Feb 2018
Posts: 1
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 26 Feb 2018, 02:55
In this question, when combining 1) and 2) could not a=0? Hence answer should be E?
PS Forum Moderator
avatar
D
Joined: 25 Feb 2013
Posts: 1217
Location: India
GPA: 3.82
GMAT ToolKit User Premium Member Reviews Badge
Re: Is a divisible by 3?  [#permalink]

Show Tags

New post 26 Feb 2018, 03:11
1
ma123 wrote:
In this question, when combining 1) and 2) could not a=0? Hence answer should be E?


Hi ma123

if a=0, then it will automatically be divisible by 3. 0 is divisible by every number. 0/3=0
GMAT Club Bot
Re: Is a divisible by 3? &nbs [#permalink] 26 Feb 2018, 03:11
Display posts from previous: Sort by

Is a divisible by 3?

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.