Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Number Theory - Factors

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
User avatar
Senior | Next Rank: 100 Posts
Posts: 43
Joined: Fri Feb 20, 2015 2:12 am
Thanked: 1 times
by ddg » Thu Apr 09, 2015 9:30 am
Please refer to the image :) Need a little help on this... Also posting my explanation along with it.
QUESTION:

Image

MY EXPLANATION:


Image

--------------------
Please help me out on this..thanks!
Last edited by ddg on Fri Apr 10, 2015 2:49 am, edited 1 time in total.
Top
Join the discussion
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10391
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Thu Apr 09, 2015 10:25 am
Hi ddg,

I'd like to know a few things about this question before I offer a solution:

1) What is the source of this question? Did it come from a GMAT book/website/CAT/etc or did it come from a math book(or equivalent)?
2) As a problem solving question, it should include 5 answer choices. What are they?

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
User avatar
Senior | Next Rank: 100 Posts
Posts: 43
Joined: Fri Feb 20, 2015 2:12 am
Thanked: 1 times

by ddg » Thu Apr 09, 2015 9:03 pm
Hi, I am so sorry, I completely forgot to mention the source and the options :)

Source: Book on CAT prep - Demystifying the Number System 1st edition
--------------
Options of the question

A) 39
B) 493
C) 439
D) 593
E) 539
Last edited by ddg on Fri Apr 10, 2015 2:52 am, edited 1 time in total.
Top
Join the discussion
User avatar
Senior | Next Rank: 100 Posts
Posts: 43
Joined: Fri Feb 20, 2015 2:12 am
Thanked: 1 times

by ddg » Thu Apr 09, 2015 9:14 pm
Also, the answer is supposed to be 493
--------------------------------------------
Consider an example: 6 and 36 where 6 = n and 36 = n(square)
then 6 has the factors = 1, 2, 3, 6 (4 in number)
and 36 had the factors = 1, 2, 3, 4, 6, 9, 12, 18, 36 (9 in number)
Now any of the factors of 6 are < 6 and hence we subtract those numbers or remove those numbers from the factors of n(square) -> we get 4, 9, 12, 18, 36 left.
Out of all of these factors, only 4 is < 6 that does NOT divide (specified according to qn to find factors < n that don't divide n).
So in an example such as this, we have only one factor.

Now considering that for this qn, n(square) has 59X35 factors = 2065 factors.
And n has 540 factors. So, subtracting them, the pool of factors we can choose from is = 2065 - 540 = 1525 factors. how do we know how many of these factors are less than n???????
Top
Join the discussion