• PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh

2 Quick Questions

This topic has 2 expert replies and 1 member reply
javzprobz Junior | Next Rank: 30 Posts Default Avatar
Joined
22 Jul 2012
Posted:
16 messages
Upvotes:
2
Target GMAT Score:
700+

2 Quick Questions

Post Wed Aug 07, 2013 8:29 am
Hi Brent,

I would appreciate it if you answer these two questions.

First one: In the video 12 of Integer Properties, you mention one useful rule for divisors. "If jk is a divisor of N, then j is a divisor of N and k is a divisor of N."

Just a few days ago, I came across this DS question, which belongs to Manhattan:

"Is n divisible by 108? 1)n is divisible by 12 2)n is divisible by 9 "

I started solving this q by saying that statement 1 is insufficient and statement 2 is also insufficient, then I said wait a minute if I consider both statements together, I can say that if n is divisible by j and if n is divisible by k, then n is divisible by j*k too.

So, I said since 12*9 is equal to 108, then the answer to the above question should be C!

However, when I read the answer explanation for this q, I saw that the correct answer is E. The explanation said that from the q we can get this, "is n=(2^2)*(3^3)*?", and from the first statement we can get this, "n=(2^2)*3*", and from the second statement we can get this, "n=3^2". The explanation said that when combining statement 1 and 2, we can't say with certainty whether the 3 factor in the first statement is one of the two 'threes' in the second statement or it is a new 3. If it is a new 3, then n will be divisible by 108. But if it is not a new 3 (meaning it is one of those threes in the second statement), then we're not sure whether n is divisible by 108. Hence E. While I really understand the given explanation by Manhattan, I would like to know whether I used that 'Divisor Rule' in the video 12 in a wrong way to get to C or if there's a sort-of limitation or consideration when using that divisor rule.

And my second question is that, again, somewhere in Manhattan I saw this DS question:

"Is p an odd integer? 1)p^2 is odd 2)root(p) is odd"

I solved this question by saying that OK p^2=p*p=odd and we know that only the product of 2 odd numbers can be odd, so p should be odd. And root(p)*root(p)=p, since root(p) is odd and odd*odd=odd, then p should be odd. Hence D. But the given correct answer was B! Sorry, I couldn't find any explanations for that B answer. Maybe the given answer by that expert was just a mistake. Do you think my way of solving this super easy question is OK and my answer is correct?

Thank you so much in advance.

  • +1 Upvote Post
  • Quote
  • Flag
Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

GMAT/MBA Expert

Post Thu Aug 08, 2013 6:12 am
You're welcome.

All the best,
Brent

_________________
Brent Hanneson – Founder of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Check out the online reviews of our course
Come see all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
javzprobz Junior | Next Rank: 30 Posts Default Avatar
Joined
22 Jul 2012
Posted:
16 messages
Upvotes:
2
Target GMAT Score:
700+
Post Wed Aug 07, 2013 10:17 pm
I seriously can't thank you enough, Brent. Thanks a million.

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post Wed Aug 07, 2013 2:26 pm
javzprobz wrote:
Hi Brent,

I would appreciate it if you answer these two questions.

First one: In the video 12 of Integer Properties, you mention one useful rule for divisors. "If jk is a divisor of N, then j is a divisor of N and k is a divisor of N."

Just a few days ago, I came across this DS question, which belongs to Manhattan:

"Is n divisible by 108? 1)n is divisible by 12 2)n is divisible by 9 "

I started solving this q by saying that statement 1 is insufficient and statement 2 is also insufficient, then I said wait a minute if I consider both statements together, I can say that if n is divisible by j and if n is divisible by k, then n is divisible by j*k too.

So, I said since 12*9 is equal to 108, then the answer to the above question should be C!

However, when I read the answer explanation for this q, I saw that the correct answer is E. The explanation said that from the q we can get this, "is n=(2^2)*(3^3)*?", and from the first statement we can get this, "n=(2^2)*3*", and from the second statement we can get this, "n=3^2". The explanation said that when combining statement 1 and 2, we can't say with certainty whether the 3 factor in the first statement is one of the two 'threes' in the second statement or it is a new 3. If it is a new 3, then n will be divisible by 108. But if it is not a new 3 (meaning it is one of those threes in the second statement), then we're not sure whether n is divisible by 108. Hence E. While I really understand the given explanation by Manhattan, I would like to know whether I used that 'Divisor Rule' in the video 12 in a wrong way to get to C or if there's a sort-of limitation or consideration when using that divisor rule.

And my second question is that, again, somewhere in Manhattan I saw this DS question:

"Is p an odd integer? 1)p^2 is odd 2)root(p) is odd"

I solved this question by saying that OK p^2=p*p=odd and we know that only the product of 2 odd numbers can be odd, so p should be odd. And root(p)*root(p)=p, since root(p) is odd and odd*odd=odd, then p should be odd. Hence D. But the given correct answer was B! Sorry, I couldn't find any explanations for that B answer. Maybe the given answer by that expert was just a mistake. Do you think my way of solving this super easy question is OK and my answer is correct?

Thank you so much in advance.
Hi javzprobz,

I'm happy to answer these questions.

Question #1
The rule " "If jk is a divisor of N, then j is a divisor of N and k is a divisor of N" is true. However, notice that this is an IF...THEN rule.
You have incorrectly used the rule in reverse. You concluded "If "j is a divisor of N and k is a divisor of N then jk is a divisor of N." There is no such rule.


Question #2
Statement 1 tells us that p^2 is odd. However, this does not mean that p is an integer.
For example, if p = √3, then p^2 is odd, but p is not odd.
For that reason, statement 1 is not sufficient.

I hope that helps.

Cheers,
Brent

_________________
Brent Hanneson – Founder of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Check out the online reviews of our course
Come see all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
Thanked by: javzprobz
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

Best Conversation Starters

1 Roland2rule 165 topics
2 lheiannie07 110 topics
3 ardz24 60 topics
4 Vincen 50 topics
5 LUANDATO 49 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

150 posts
2 image description GMATGuruNY

The Princeton Review Teacher

125 posts
3 image description Jeff@TargetTestPrep

Target Test Prep

120 posts
4 image description Rich.C@EMPOWERgma...

EMPOWERgmat

116 posts
5 image description Scott@TargetTestPrep

Target Test Prep

100 posts
See More Top Beat The GMAT Experts