A Few Questions

Ask your questions about GMAT Prep Now products/services here
This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 16
Joined: 22 Jul 2012
Location: Famagusta
Thanked: 2 times

A Few Questions

by javzprobz » Thu Jul 25, 2013 12:54 pm
Hi Brent,

I have a few questions, so I start with the first one. In the video 38 of Integer Properties module, we have a DS q. You don't rule out the first statement because you say 5J should have prime factorization of 5*?*?*?*?, and 3k should have prime factorization of 3*?*?*?*?. And since the first statement says that GCD of 5k and 3J is 30, we know that they both should have a 5*3*2 common in their prime factorization. And when we divide 5K by 5 and 3J by 3, we would have K=2*3*?*? and J=2*5*?*?. And we know that none of the prime factors in place of question marks should be common between K and J (otherwise GCD of 5K and 3J wouldn't be 30). So now the GCD of K and J is 2. So you conclude that statement 1 is sufficient to answer the question since it gives us only one GCD. However, what if 5K's prime factorization was like this: "5*2*3*5", and 3J's prime factorization was like this: "3*2*5*3". As we can see they still have the GCD of 30. And when we divide 5k by 5 and 3J by 3, we would have K=2*3*5 and J=2*3*5. So their GCD is 30 now! So I think as you rule out the second statement by saying that 2K may or may not have a 2 in its prime factorization, I suppose we can say the same thing for the statement 1 about 5K and 3J. So I thought we should have ruled out the first statement as well since it can give us more than one answer, hence E. Am I making a mistake here? What am I missing?

My second question is about the number of RC questions that accompany a passage on the GMAT. In the first video of RC module, you mention that short passages TYPICALLY get 3 questions, and long passages TYPICALLY get 4 questions. But on the Official Guide (13 ed.), for example, we have questions 75,76,77,78,79,80,81,82, and 83 all for one passage (we have a lot of series of 6,7, or 8 questions that are asked from one passage on the OG 13). So I was wondering if on test day I may have a RC passage followed by 6,7,8, or 9 qs. Sorry if this question is a little bit naive. I tried to see if I can find a post that asks the same thing in RC forum.

And my last question is a little bit out of scope of this forum, but I'll ask it anyway. I received all the 60 emails of The 60-Day GMAT Study Guide of BTG a year ago (in July, so it has Integrated Reasoning days). However, I am now using these emails as my GMAT study plan. So I was wondering if you have made any modifications on these emails or if you have changed something. If so, please let me know, because I would like to know those even little changes that you might have made on this 60-day guide, so I can follow the updated 60-day BTG guide. Thanks a lot in advance.

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 15865
Joined: 08 Dec 2008
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1267 members
GMAT Score:770

by [email protected] » Sat Jul 27, 2013 10:29 am
javzprobz wrote:In the video 38 of Integer Properties module, we have a DS q. You don't rule out the first statement because you say 5J should have prime factorization of 5*?*?*?*?, and 3k should have prime factorization of 3*?*?*?*?. And since the first statement says that GCD of 5k and 3J is 30, we know that they both should have a 5*3*2 common in their prime factorization. And when we divide 5K by 5 and 3J by 3, we would have K=2*3*?*? and J=2*5*?*?. And we know that none of the prime factors in place of question marks should be common between K and J (otherwise GCD of 5K and 3J wouldn't be 30). So now the GCD of K and J is 2. So you conclude that statement 1 is sufficient to answer the question since it gives us only one GCD. However, what if 5K's prime factorization was like this: "5*2*3*5", and 3J's prime factorization was like this: "3*2*5*3". As we can see they still have the GCD of 30. And when we divide 5k by 5 and 3J by 3, we would have K=2*3*5 and J=2*3*5. So their GCD is 30 now! So I think as you rule out the second statement by saying that 2K may or may not have a 2 in its prime factorization, I suppose we can say the same thing for the statement 1 about 5K and 3J. So I thought we should have ruled out the first statement as well since it can give us more than one answer, hence E. Am I making a mistake here? What am I missing?
Hi Javzprobz,

You're absolutely right! You're the first person to catch that error. We have since replaced that video with a slightly different question. Thanks for the heads up!!
javzprobz wrote: My second question is about the number of RC questions that accompany a passage on the GMAT. In the first video of RC module, you mention that short passages TYPICALLY get 3 questions, and long passages TYPICALLY get 4 questions. But on the Official Guide (13 ed.), for example, we have questions 75,76,77,78,79,80,81,82, and 83 all for one passage (we have a lot of series of 6,7, or 8 questions that are asked from one passage on the OG 13). So I was wondering if on test day I may have a RC passage followed by 6,7,8, or 9 qs. Sorry if this question is a little bit naive. I tried to see if I can find a post that asks the same thing in RC forum.
For each RC question, the test-makers create several questions. These questions range in difficulty, so the 3 or 4 questions that test-takers see on test day will depend on their level of expertise. So, even though RC passages typically have 3 or 4 questions, the test-makers have decided to include several questions (of varying difficulty) in the Official Guide.

javzprobz wrote: And my last question is a little bit out of scope of this forum, but I'll ask it anyway. I received all the 60 emails of The 60-Day GMAT Study Guide of BTG a year ago (in July, so it has Integrated Reasoning days). However, I am now using these emails as my GMAT study plan. So I was wondering if you have made any modifications on these emails or if you have changed something. If so, please let me know, because I would like to know those even little changes that you might have made on this 60-day guide, so I can follow the updated 60-day BTG guide. Thanks a lot in advance.
The last revision to the 60-Day Guide was made in June, 2012. So, you have the most up-to-date version.

Cheers and thanks again,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image

Junior | Next Rank: 30 Posts
Posts: 16
Joined: 22 Jul 2012
Location: Famagusta
Thanked: 2 times

by javzprobz » Sat Jul 27, 2013 11:04 am
Thank you so much, Brent.