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• ### $450 Tuition Credit & Official CAT Packs FREE November 15, 2018 November 15, 2018 10:00 PM MST 11:00 PM MST EMPOWERgmat is giving away the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) # Two different primes may be said to “rhyme” around an integer if they  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message TAGS: ### Hide Tags Senior Manager Status: Up again. Joined: 31 Oct 2010 Posts: 496 Concentration: Strategy, Operations GMAT 1: 710 Q48 V40 GMAT 2: 740 Q49 V42 Two different primes may be said to"rhyme" around an integer [#permalink] ### Show Tags 03 Jan 2011, 09:58 4 13 00:00 Difficulty: 95% (hard) Question Stats: 32% (02:49) correct 68% (02:06) wrong based on 459 sessions ### HideShow timer Statistics Two different primes may be said to"rhyme" around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? A. 12 B. 15 C. 17 D. 18 E. 20 Source: MGMAT Heaven knows what I'll do if I encounter such a question on GMAT!! It is solvable no doubt but very time consuming.. Please do post the time you take to solve this question.. I took 1.4 minutes to grasp the question, then left it as I thought it would eat away the valuable remaining time on the test. _________________ My GMAT debrief: http://gmatclub.com/forum/from-620-to-710-my-gmat-journey-114437.html ##### Most Helpful Expert Reply Math Expert Joined: 02 Sep 2009 Posts: 50544 Two different primes may be said to"rhyme" around an integer [#permalink] ### Show Tags 03 Jan 2011, 12:30 8 3 gmatpapa wrote: Two different primes may be said to"rhyme" around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? 1. 12 2. 15 3. 17 4. 18 5. 20 Source: MGMAT Heaven knows what I'll do if I encounter such a question on GMAT!! It is solvable no doubt but very time consuming.. Please do post the time you take to solve this question.. I took 1.4 minutes to grasp the question, then left it as I thought it would eat away the valuable remaining time on the test. As per definition two different primes $$p_1$$ and $$p_2$$ are "rhyming primes" if $$n-p_1=p_2-n$$, for some integer $$n$$ --> $$2n=p_1+p_2$$. So twice the number $$n$$ must equal to the sum of two different primes, one less than $$n$$ and another more than $$n$$. Let's test each option: A. 12 --> 2*12=24 --> 24=5+19=7+17=11+13: 6 rhyming primes (start from the least prime and see whether we can get the sum of 24 by adding another prime more than 12 to it); B. 15 --> 2*15=30 --> 30=7+23=11+19=13+17: 6 rhyming primes; C. 17 --> 2*17=34 --> 34=3+31=5+29=11+23: 6 rhyming primes; D. 18 --> 2*18=36 --> 36=5+31=7+29=13+23=17+19: 8 rhyming primes; E. 20 --> 2*20=40 --> 40=3+37=11+29=17+23: 6 rhyming primes. Answer: D. _________________ ##### Most Helpful Community Reply Board of Directors Joined: 01 Sep 2010 Posts: 3312 Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 11 Mar 2012, 12:45 3 6 Two different primes may be said to “rhyme” around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? (A) 12 (B) 15 (C) 17 (D) 18 (E) 20 _________________ ##### General Discussion Manager Joined: 13 Aug 2010 Posts: 165 Re: rhyming primes [#permalink] ### Show Tags 04 Jan 2011, 01:23 great explanation Bunel, thanks a lot..... and a nice question Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 8521 Location: Pune, India Re: rhyming primes [#permalink] ### Show Tags 04 Jan 2011, 18:32 3 1 gmatpapa wrote: Two different primes may be said to"rhyme" around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? 1. 12 2. 15 3. 17 4. 18 5. 20 Source: MGMAT Heaven knows what I'll do if I encounter such a question on GMAT!! It is solvable no doubt but very time consuming.. Please do post the time you take to solve this question.. I took 1.4 minutes to grasp the question, then left it as I thought it would eat away the valuable remaining time on the test. Alternative solution: Since we are concerned with integers between 1 and 20, write down the primes till 40. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 (you should be very comfortable with the first few primes... ) 2, 3, 5, 7, 11, 12, 13, 17, 19, 23, 29, 31, 37 - Three pairs (11,13), (7,17), (5, 19) 2, 3, 5, 7, 11, 13, 15, 17, 19, 23, 29, 31, 37 - Three pairs (13, 17), (11, 19), (7, 23) 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 - Three pairs (11, 23), (5, 29), (3, 31) 2, 3, 5, 7, 11, 13, 17, 18, 19, 23, 29, 31, 37 - Four pairs (17, 19), (13, 23), (7, 29), (5, 31) 2, 3, 5, 7, 11, 13, 17, 19, 20, 23, 29, 31, 37 - definitely cannot be more than 4 since there are only 4 primes more than 20. So must be less than 4 pairs. Ignore. Answer (D). It doesn't take too much time to look for equidistant pairs... _________________ Karishma Veritas Prep GMAT Instructor Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options > GMAT self-study has never been more personalized or more fun. Try ORION Free! Math Expert Joined: 02 Sep 2009 Posts: 50544 Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 11 Mar 2012, 13:12 6 1 Check other Special Numbers and Sequences questions in our Special Questions Directory. _________________ Board of Directors Joined: 01 Sep 2010 Posts: 3312 Re: Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 11 Mar 2012, 14:35 Thanks Bunuel. This is the first time I see something like that in a question. Intersting is your formula because I don't understand why if we had 20 numbers we worked with 40. Can you give me some links to investigate a little further this concept ??' Thnaks again for explanation. _________________ Math Expert Joined: 02 Sep 2009 Posts: 50544 Re: Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 11 Mar 2012, 23:01 2 carcass wrote: Thanks Bunuel. This is the first time I see something like that in a question. Intersting is your formula because I don't understand why if we had 20 numbers we worked with 40. Can you give me some links to investigate a little further this concept ??' Thnaks again for explanation. There is no special concept behind it. We have that: $$2n=p_1+p_2$$, for some integer $$n$$. Answer choices give different values of $$n$$ and we should find out which $$n$$ has the greatest number of distinct rhyming primes around it. When plugging values from answer choices for $$n$$ in $$2n=p_1+p_2$$, you'll have $$2n$$ to wok with since there is $$2n$$ in the formula. Hope it's clear. _________________ Intern Joined: 22 Apr 2013 Posts: 1 Re: rhyming primes [#permalink] ### Show Tags 20 May 2013, 22:43 VeritasPrepKarishma wrote: gmatpapa wrote: Two different primes may be said to"rhyme" around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? 1. 12 2. 15 3. 17 4. 18 5. 20 Source: MGMAT Heaven knows what I'll do if I encounter such a question on GMAT!! It is solvable no doubt but very time consuming.. Please do post the time you take to solve this question.. I took 1.4 minutes to grasp the question, then left it as I thought it would eat away the valuable remaining time on the test. Alternative solution: Since we are concerned with integers between 1 and 20, write down the primes till 40. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 (you should be very comfortable with the first few primes... ) 2, 3, 5, 7, 11, 12, 13, 17, 19, 23, 29, 31, 37 - Three pairs (11,13), (7,17), (5, 19) 2, 3, 5, 7, 11, 13, 15, 17, 19, 23, 29, 31, 37 - Three pairs (13, 17), (11, 19), (7, 23) 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 - Three pairs (11, 23), (5, 29), (3, 31) 2, 3, 5, 7, 11, 13, 17, 18, 19, 23, 29, 31, 37 - Four pairs (17, 19), (13, 23), (7, 29), (5, 31) 2, 3, 5, 7, 11, 13, 17, 19, 20, 23, 29, 31, 37 - definitely cannot be more than 4 since there are only 4 primes more than 20. So must be less than 4 pairs. Ignore. Answer (D). It doesn't take too much time to look for equidistant pairs... why are we considering till 40?? I did not get it Senior Manager Joined: 16 Dec 2011 Posts: 326 Re: rhyming primes [#permalink] ### Show Tags 21 May 2013, 01:14 royal wrote: why are we considering till 40?? I did not get it As the highest integer, for which rhyming pair to be found, is 20, we need to consider equal range below the number 20 and above the number 20. In fact, we need to consider the range (2,38) as the lowest prime is 2. Intern Joined: 12 Aug 2014 Posts: 10 Location: United States Concentration: Strategy, General Management GMAT 1: 710 Q50 V35 GMAT 2: 720 Q49 V40 WE: Other (Consulting) Re: Two different primes may be said to"rhyme" around an integer [#permalink] ### Show Tags 21 Dec 2014, 05:29 Bunuel and Karishma, 17 has four set of rhyming primes. You both haven't considered (3,31) as a possible answer. Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 8521 Location: Pune, India Re: Two different primes may be said to"rhyme" around an integer [#permalink] ### Show Tags 21 Dec 2014, 20:29 1 anon1111 wrote: Bunuel and Karishma, 17 has four set of rhyming primes. You both haven't considered (3,31) as a possible answer. Both Bunuel and I have considered 3 and 31 as rhyming primes for 17 in our solutions above. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 - Three pairs (11, 23), (5, 29), (3, 31) _________________ Karishma Veritas Prep GMAT Instructor Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options > GMAT self-study has never been more personalized or more fun. Try ORION Free! Senior Manager Status: Math is psycho-logical Joined: 07 Apr 2014 Posts: 422 Location: Netherlands GMAT Date: 02-11-2015 WE: Psychology and Counseling (Other) Re: Two different primes may be said to"rhyme" around an integer [#permalink] ### Show Tags 30 Dec 2014, 11:07 Hello, I wanted to share how I ended up with the correct answer. It is probably a lucky choice, but just in case I wanted to share. So, I didn't see the connection with the mean (even though statistics is my biggest strength). What I did was to first find the primes up to 20, just to see if there is a pattern that makes sense. So, I lined them up, smaller to larger, and tried to find a number that is between 1 and 20. For me this meant 1<x<20, so I wanted a number that is one of these: 2,3,4....,19. Then, I realised that there is no upper limmit to the primes - so there is no reason why they should stop at 19. What I realised then, is that the number that has most primes should be the highest possible in the range we are given: one of 2,3,4,....,19. So, 19 being the highest value, it is logical that this one would have the most primes around it. I rejected 20, because of the range, so I chose 18 (D), because it was the second highest. Does it make any sense? CEO Status: GMATINSIGHT Tutor Joined: 08 Jul 2010 Posts: 2689 Location: India GMAT: INSIGHT WE: Education (Education) Re: Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 22 Oct 2015, 05:55 4 carcass wrote: Two different primes may be said to “rhyme” around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it? (A) 12 (B) 15 (C) 17 (D) 18 (E) 20 How to deal with ??? Just solve it by checking every option Answer : Option D Attachments File comment: www.GMATinsight.com sol2.jpg [ 102.15 KiB | Viewed 4782 times ] _________________ Prosper!!! GMATinsight Bhoopendra Singh and Dr.Sushma Jha e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772 Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi http://www.GMATinsight.com/testimonials.html ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 12841 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: Two different primes may be said to “rhyme” around an integer if they [#permalink] ### Show Tags 07 Mar 2018, 19:37 Hi All, This question requires a bit of a tactical approach combined with "brute force." The answers to this question provide 5 possible values that COULD have the GREATEST number of rhyming primes, so we just have to figure out which one it is. We can't afford to stare at the problem though; to be efficient, we have to get in and throw some punches. We're told to look for prime numbers that are equidistant from a number, but we're limited to numbers from 1 to 20, inclusive. Let's list out the primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 (nothing above 40 is required, since there wouldn't be a matching rhyme prime on the other "side" of the number) Logically, the correct answer will probably be one of the bigger integers, since those values allow for a greater number of primes that are "lower." We can quickly check them all though. A: 12 - 5&19, 7&17, 11&13 B: 15 - 7&23, 11&19, 13&17 C: 17 - 3&31, 5&29, 11&23 D: 18 - 5&31, 7&29, 13&23, 17&19 E: 20 - 3&37, 11&29, 17&23 Final Answer: GMAT assassins aren't born, they're made, Rich _________________ 760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com # Rich Cohen Co-Founder & GMAT Assassin Special Offer: Save$75 + GMAT Club Tests Free
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Re: Two different primes may be said to “rhyme” around an integer if they  [#permalink]

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19 Apr 2018, 14:48
Top Contributor
gmatpapa wrote:
Two different primes may be said to"rhyme" around an integer if they are the same distance from the integer on the number line. For instance, 3 and 7 rhyme around 5. What integer between 1 and 20, inclusive, has the greatest number of distinct rhyming primes around it?

A. 12
B. 15
C. 17
D. 18
E. 20

If two numbers are rhyming primes, then the integer they rhyme around will be the AVERAGE of the two primes.

For example, 3 and 7 rhyme around 5. Notice that the AVERAGE of 3 and 7 is 5.
Likewise, 5 and 23 rhyme around 14, and the AVERAGE of 5 and 23 is 14.

Now onto the solution...

List several primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41,....

A)12
For 12 to be the integer that two primes rhyme around, we need 2 primes that have an AVERAGE of 12. In other words, we need 2 primes that ADD to 24. Now check the list of primes to find pairs that satisfy this condition.
We get: 5 & 19, 7 & 17, 11 & 13
Total of 3 pairs.

B)15
So, we need 2 distinct primes that ADD to 30.
We get: 7 & 23, 11 & 19, 13 & 17
Total of 3 pairs.

C)17
So, we need 2 distinct primes that ADD to 34.
We get: 3 & 31, 5 & 29, 11 & 23
Total of 3 pairs.

D)18
So, we need 2 distinct primes that ADD to 36.
We get: 5 & 31, 7 & 29, 13 & 23, 17 & 19
Total of 4 pairs.

E)20
So, we need 2 distinct primes that ADD to 40.
We get: 3 & 37, 11 & 29, 17 & 23
Total of 3 pairs.

Cheers,
Brent
_________________

Brent Hanneson – GMATPrepNow.com

Re: Two different primes may be said to “rhyme” around an integer if they &nbs [#permalink] 19 Apr 2018, 14:48
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