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.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Want to score 90 percentile or higher on GMAT CR? Attend this free webinar to learn how to pre-think assumptions and solve the most challenging questions in less than 2 minutes.

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

31 Aug 2016, 07:30

1

Stat 1: 80 < y < 95, We get both prime and nonprime numbers =Insufficient.

Stat 2: y= 3x + 1, the result must be multiple of y, and x is positive integer, X and y are unknown =Insufficient.

both statements the result must be multiple of y , and x is positive integer, possible values of y for x to be integer are 82,85,88,91,94, all are nonprimes= sufficient condition to answer the question,

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

31 Aug 2016, 08:05

1

Top Contributor

2

Bunuel wrote:

Is the positive integer y a prime number?

(1) 80 < y < 95 (2) y = 3x + 1, where x is a positive integer

Target question:Is y a prime number?

Given: y is a positive integer

Statement 1: 80 < y < 95 This statement doesn't FEEL sufficient, so I'll TEST some values. There are several values of y that satisfy statement 1. Here are two: Case a: y = 81, in which case y is NOT prime Case b: y = 83, in which case y IS prime Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: y = 3x + 1, where x is a positive integer There are several values of y that satisfy statement 2. Here are two: Case a: y = (3)(1) + 1 = 4, in which case y is NOT prime Case b: y = (3)(2) + 1 = 7, in which case y IS prime Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined Let's list ALL possible values of y. y = (3)(27) + 1 = 82 (82 is NOT prime) y = (3)(28) + 1 = 85 (85 is NOT prime) y = (3)(29) + 1 = 88 (88 is NOT prime) y = (3)(30) + 1 = 91 (91 is NOT prime)(91 = 13 times 7) y = (3)(31) + 1 = 94 (94 is NOT prime) So, we can conclude that y is NOT prime Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

01 Sep 2016, 19:16

Answer should be both statements together are sufficient to get the answer . From first statement you are getting many prime numbers not a definite value , but if you use y=3x+1 then the only prime number between 80 and 95 is 91 when X=30 which will give you 91 , hence addresses first statement as well

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

01 Sep 2016, 23:15

vikasku3087 wrote:

Answer should be both statements together are sufficient to get the answer . From first statement you are getting many prime numbers not a definite value , but if you use y=3x+1 then the only prime number between 80 and 95 is 91 when X=30 which will give you 91 , hence addresses first statement as well

That is incorrect mate. If you use both statements together, it proves none of the numbers are prime. If you get even one number as prime, you're getting 2 answers hence, insufficient.

In this case, all the numbers are not prime, and that's why the 1) & 2) are sufficient together and C is the answer. Be careful with this when solving DS questions.

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

02 Sep 2016, 03:59

Question has a question mark - it is asking that whether y is prime number or not? So not is also an answer . It is simple case of putting number in second equation and testing -

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

04 Oct 2016, 17:26

Top Contributor

sukeshap wrote:

Bunuel wrote:

Is the positive integer y a prime number?

(1) 80 < y < 95 (2) y = 3x + 1, where x is a positive integer

Anybody please tell how C is the correct answer. As per me, E is the correct answer

To demonstrate that the correct answer is E, you must show that there are two possible values for y that satisfy BOTH statements AND yield conflicting answer choices to the target question (is y prime?). When we combine the statements, we can see that y can equal 82 or 85 or 88 or 91 or 94 In all 5 possible cases, the answer to the target question is the same; y is not prime. In other words, we can be CERTAIN that the answer to the target question is NO - y is not prime.

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

06 Oct 2017, 09:00

Bunuel wrote:

Is the positive integer y a prime number?

(1) 80 < y < 95 (2) y = 3x + 1, where x is a positive integer

each alone is obviously insuff

both together

the min value of x in y = 3x+1 is 27.... to satisfy 80<y<95 , all primes >3 are in the form 6n+1 or 6n-1 , i.e. before or after a multiple of 6

in the given range multiples of 6 are 84 , 90 , check around 84 and 90 ( 83,85) and (89,91) ... of which only 85 and 91 satisfy the form (3x+1)both of which are non prime .... suff

Re: Is the positive integer y a prime number?
[#permalink]

Show Tags

06 Jan 2019, 06:01

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________