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

It is currently 12 Nov 2019, 19:08

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

If j > 1, is integer j a prime number? (1) When j is divided by 3, th

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

Hide Tags

Find Similar Topics 
Senior Manager
Senior Manager
User avatar
Joined: 12 Aug 2015
Posts: 280
Concentration: General Management, Operations
GMAT 1: 640 Q40 V37
GMAT 2: 650 Q43 V36
GMAT 3: 600 Q47 V27
GPA: 3.3
WE: Management Consulting (Consulting)
If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 09 Jan 2016, 11:04
4
7
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

58% (01:37) correct 42% (01:39) wrong based on 242 sessions

HideShow timer Statistics

If j > 1, is integer j a prime number?

(1) When j is divided by 3, the remainder is 1.

(2) When j is divided by 2, the remainder is 1.

_________________
KUDO me plenty
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 12 Sep 2015
Posts: 4055
Location: Canada
Re: If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 09 Jan 2016, 11:33
2
1
Quote:
If j > 1, is integer j a prime number?

(1) When j is divided by 3, the remainder is 1.

(2) When j is divided by 2, the remainder is 1.


When it comes to remainders, we have a nice rule that says:

If N divided by D, leaves remainder R, then the possible values of N are R, R+D, R+2D, R+3D,. . . etc.

For example, if k divided by 5 leaves a remainder of 1, then the possible values of k are: 1, 1+5, 1+(2)(5), 1+(3)(5), 1+(4)(5), . . . etc.

Okay, now onto the question.

Target question: Is integer j a prime number?

Statement 1: When j is divided by 3, the remainder is 1.
Possible values of j: 4, 7, 10, 13, 16, 19, 22, 25...
As you can see, some values of j are prime and some are not.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: When j is divided by 2, the remainder is 1.
Possible values of j: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, ...
As you can see, some values of j are prime and some are not.
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined:
From statement 1: j could equal 4, 7, 10, 13, 16, 19, 22, 25...
From statement 2: j could equal 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, ...

Some numbers that satisfy both statements are 7, 13, 19, 25, . . .
Once again, some values of j are prime and some are not.
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
Image
Intern
Intern
avatar
Joined: 07 Dec 2015
Posts: 7
If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post Updated on: 09 Jan 2016, 11:58
1
Took me a little over a min.

Statement 1. All this tells us is that j is not divisible by 3. Not all numbers not divisible by 3 are prime. e.g. 10, not divisible by 3 and is composite (not prime).
Statement 2. Similarly, all this tells us is that j is not divisible by 2, not all numbers not divisible by 2 are prime. e.g. 15, 25.

Statement 1 + 2 if j>1, and not divisible by 3 or 2, is j prime? Ans... Not necessarily, though it might be tempting to think that j is indeed prime. lets think of examples where a number is not divisible by 2 or 3. e.g 17(prime), 19 (prime), 23(prime, 25 (NOT PRIME).

Ans - E.

Hope it is clear.

Originally posted by Lettherebelight on 09 Jan 2016, 11:22.
Last edited by Lettherebelight on 09 Jan 2016, 11:58, edited 1 time in total.
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 8125
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 10 Jan 2016, 19:24
1
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.


If j > 1, is integer j a prime number?

(1) When j is divided by 3, the remainder is 1.

(2) When j is divided by 2, the remainder is 1.

In the original condition, there is 1 variable(x), which should match with the number of equation. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer.
For 1), j=7 -> yes, j=25 -> no, which is not sufficient.
For 2), =7-> yes, j=25 -> no, which is not sufficient.
When 1) & 2), j=7 -> yes, j=25 -> no, which is not sufficient. Therefore, the answer is E.


 For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Current Student
User avatar
Joined: 18 Jul 2015
Posts: 39
Location: Brazil
Concentration: General Management, Strategy
GMAT 1: 640 Q39 V38
GMAT 2: 700 Q47 V38
Re: If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 11 Jan 2016, 16:43
1
Statement 1 - J could be 4, 7, 10, 13, 16, 19, 22, 25, 28 (keep adding 3) . NOT SUFF.
Statement 2 - J could be 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27 (keep adding 2). NOT SUFF.
Statement 1 and 2 - J could be 7, 13, 19 and 25 (which is not a prime number) . NOT SUFF.

Hope it helps.
Current Student
User avatar
D
Joined: 12 Aug 2015
Posts: 2549
Schools: Boston U '20 (M)
GRE 1: Q169 V154
GMAT ToolKit User
Re: If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 22 Mar 2016, 09:35
1
VP
VP
User avatar
D
Joined: 14 Feb 2017
Posts: 1266
Location: Australia
Concentration: Technology, Strategy
GMAT 1: 560 Q41 V26
GMAT 2: 550 Q43 V23
GMAT 3: 650 Q47 V33
GMAT 4: 650 Q44 V36
GMAT 5: 650 Q48 V31
GPA: 3
WE: Management Consulting (Consulting)
Reviews Badge CAT Tests
If j > 1, is integer j a prime number? (1) When j is divided by 3, th  [#permalink]

Show Tags

New post 21 Aug 2019, 16:57
Statement 1
j could be : ,4,7,10,13,16,19,22,25
non-prime and prime

Statement 2:
J could be: , 3, 5, 7, 9,11,13,15,17,19,21,23,25
non-prime and prime

Combined, j could be 7 or 25 from what we know - prime or non prime

Insufficient
_________________
Goal: Q49, V41

+1 Kudos if I have helped you
GMAT Club Bot
If j > 1, is integer j a prime number? (1) When j is divided by 3, th   [#permalink] 21 Aug 2019, 16:57
Display posts from previous: Sort by

If j > 1, is integer j a prime number? (1) When j is divided by 3, th

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





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