NEW HERE? LEARN MORE
closeclose
Last visit was: 26 Apr 2024, 15:46 It is currently 26 Apr 2024, 15:46
Decision Tracker
My Rewards
New posts
New comers' posts

Close
GMAT Club Daily Prep
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

How many of the positive factors of 42 are not factors of 56?

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
kashishh
Manager
Manager
Joined: 02 Jun 2011
Posts: 95
Own Kudos [?]: 376 [8]
Given Kudos: 11
Send PM
How many of the positive factors of 42 are not factors of 56? [#permalink] New post   Updated on: 23 Aug 2015, 11:21
8
Bookmarks
00:00
A
B
C
D
E

Difficulty:

55% (hard)

Question Stats:

57% (01:36) correct 43% (01:25) wrong based on 229 sessions
Hide Show timer Statistics
How many of the positive factors of 42 are not factors of 56?

A. 1
B. 2
C. 3
D. 4
E. 5
ShowHide Answer
Official Answer
D

Originally posted by kashishh on 07 Aug 2011, 07:18.
Last edited by Bunuel on 23 Aug 2015, 11:21, edited 2 times in total.
Renamed the topic and edited the question.
avatar
B
onayemi
Intern
Intern
Joined: 02 Aug 2011
Posts: 4
Own Kudos [?]: 3 [0]
Given Kudos: 4
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:27
Factors of 42 - 1,2,3,6,7,14,42
factors of 56 - 1,2,4,7,8,14,28,56

Comparing both, we have three factors of 42 which are not factors of 56 - 3,6,42 .
The answer is 3. Pls check your options again - D $ E are same.
User avatar
fluke
Retired Moderator
Joined: 20 Dec 2010
Posts: 1114
Own Kudos [?]: 4702 [2]
Given Kudos: 376
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:31
2
Kudos
kashishh wrote:
How many +ve factors of 42 are not factors of 56.
a.) 1 b.) 2 c.) 4 d.) 5 e) 5

pls explain !


\(42=2*3*7\)
\(56=2^3*7\)

Total factors of 42=2*2*2=8

Common factors should be the HCF=\(2^1*7^1\)
Number of factors=2*2=4

Not Common factor=8-4=4

Ans: "C"
**********************************

For more on how to count factors, visit GMAT Club Math Book- Number Properties.
User avatar
kashishh
Manager
Manager
Joined: 02 Jun 2011
Posts: 95
Own Kudos [?]: 376 [0]
Given Kudos: 11
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:36
why total factors as 8, it should be 7?
why do you multiply 2*2 and subtract from 8?
User avatar
kashishh
Manager
Manager
Joined: 02 Jun 2011
Posts: 95
Own Kudos [?]: 376 [0]
Given Kudos: 11
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:39
to onayemi - yes i got it your way but the book has solved it fluke way!. sorry for e.) is 3
User avatar
fluke
Retired Moderator
Joined: 20 Dec 2010
Posts: 1114
Own Kudos [?]: 4702 [1]
Given Kudos: 376
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:42
1
Kudos
kashishh wrote:
why total factors as 8, it should be 7?
why do you multiply 2*2 and subtract from 8?


Already suggested.
Please visit: math-number-theory-88376.html

Look for section: "Finding the Number of Factors of an Integer"

If we find the total factors of an integer and subtract the common factors, won't we find the uncommon factor?

Also: the integers 42 and 56 are not perfect squares. So, they can't have odd number of factors i.e. 7(odd).
User avatar
timeishere
Intern
Intern
Joined: 03 Jul 2011
Posts: 15
Own Kudos [?]: 29 [0]
Given Kudos: 0
 Q50  V36
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:48
Hi,
Read the ques again. It is asking which +ve factors of 42 are not factors of 56.
Factors of 42 = 1,2,3,6,7,14,21,42
Factors of 56 = 1,2,4,7,8,14,28,56

Factors of 42 which are not factors of 56 = 3,6,21,42 == 4 Factors
Hence C
Check the OA again.
avatar
B
onayemi
Intern
Intern
Joined: 02 Aug 2011
Posts: 4
Own Kudos [?]: 3 [0]
Given Kudos: 4
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 07:53
[Kashish , you r correct! My approach was actually okay except for the ommission of 21 in my list of factors for 42. Adding that, the answer is 4.
User avatar
kashishh
Manager
Manager
Joined: 02 Jun 2011
Posts: 95
Own Kudos [?]: 376 [0]
Given Kudos: 11
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   07 Aug 2011, 08:02
got it timeshere,thnx!
thx fluke - i wl study up ur suggested site.
User avatar
144144
Manager
Manager
Joined: 08 Nov 2010
Posts: 204
Own Kudos [?]: 496 [0]
Given Kudos: 161
 Q50  V41
GPA: 3.9
WE 1: Business Development
Send PM
GMAT ToolKit User
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   08 Aug 2011, 10:19
fluke wrote:
kashishh wrote:
How many +ve factors of 42 are not factors of 56.
a.) 1 b.) 2 c.) 4 d.) 5 e) 5

pls explain !


\(42=2*3*7\)
\(56=2^3*7\)

Total factors of 42=2*2*2=8

Common factors should be the HCF=\(2^1*7^1\)
Number of factors=2*2=4

Not Common factor=8-4=4

Ans: "C"
**********************************

For more on how to count factors, visit GMAT Club Math Book- Number Properties.



Amazing solution. I saved it by counting the multiples of 3 which is missing from 56's factors. +1 fluke
User avatar
D
stonecold
Alum
Joined: 12 Aug 2015
Posts: 2282
Own Kudos [?]: 3132 [0]
Given Kudos: 893
Schools: Boston U '20 (M)
GRE 1: Q169 V154
Send PM
GMAT ToolKit User
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   14 Mar 2016, 08:55
Easiest way out => count them => 3,6,21,42
hence 4
User avatar
S
14101992
Manager
Manager
Joined: 22 Jun 2016
Posts: 187
Own Kudos [?]: 566 [0]
Given Kudos: 10
Send PM
Reviews Badge
Re: How many positive factors of 42 are not factors of 56? [#permalink] New post   24 Jul 2016, 10:11
42=2*3*7.

So, total number of factors for 42 = 2*2*2 = 8

factors for 42 = 1,2,3,6,7,14,21 and 42

56=2*2*2*7

So, total number of factors for 56 = 4*2 = 8

factors of 56 = 1,2,4,7,8,14,28 and 56.

Factors same in 42 and 56 are 1,2,7 and 14.

Hence, answer will be D.
User avatar
DensetsuNo
Manager
Manager
Joined: 11 Oct 2015
Status:2 months to go
Posts: 91
Own Kudos [?]: 857 [0]
Given Kudos: 38
Schools: HBS 2+2 '22 MIT Sloan MSMS"18
GMAT 1: 730 Q49 V40
GPA: 3.8
Send PM
Re: How many positive factors of 42 are not factors of 56? [#permalink] New post   24 Jul 2016, 11:07
42= 2*3*7
Since the only difference between 42 and 56 is that 56 doesn't have 3 among its prime factors, the answer has to be 4.

3*1 = 3
2*3 = 6
7*3 = 21
2*7*3 = 42

Answer D.
User avatar
B
law258
Senior Manager
Senior Manager
Joined: 05 Sep 2016
Status:DONE!
Posts: 274
Own Kudos [?]: 101 [0]
Given Kudos: 283
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   29 Nov 2016, 22:02
factors of 42
1, 42
2, 21
3, 14
7, 6

factors of 56
1, 56
2, 28
4, 14
7, 8

1,2,7,14 are all common to 56 --> so, eliminate --> we're left with 4 factors for 42.

D.
User avatar
L
ScottTargetTestPrep
Target Test Prep Representative
Joined: 14 Oct 2015
Status:Founder & CEO
Affiliations: Target Test Prep
Posts: 18767
Own Kudos [?]: 22062 [0]
Given Kudos: 283
Location: United States (CA)
Send PM
Re: How many of the positive factors of 42 are not factors of 56? [#permalink] New post   03 Oct 2019, 12:25
Expert Reply
kashishh wrote:
How many of the positive factors of 42 are not factors of 56?

A. 1
B. 2
C. 3
D. 4
E. 5



42 = 2 x 3 x 7

56 = 7 x 8 = 7 x 2^3

So, the factors of 42 that are not of 56 are 3, 3 x 2, 3 x 7, and 2 x 3 x 7.

Answer: D
GMAT Club Bot
gmatclubot
Re: How many of the positive factors of 42 are not factors of 56? [#permalink]
03 Oct 2019, 12:25
Moderators:
Bunuel
Math Expert
92948 posts
yashikaaggarwal
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions