GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 12 Dec 2018, 04:01

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

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

Events & Promotions

Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• The winning strategy for 700+ on the GMAT

December 13, 2018

December 13, 2018

08:00 AM PST

09:00 AM PST

What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.
• GMATbuster's Weekly GMAT Quant Quiz, Tomorrow, Saturday at 9 AM PST

December 14, 2018

December 14, 2018

09:00 AM PST

10:00 AM PST

10 Questions will be posted on the forum and we will post a reply in this Topic with a link to each question. There are prizes for the winners.

M14-04

Author Message
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 51123

Show Tags

15 Sep 2014, 23:50
00:00

Difficulty:

45% (medium)

Question Stats:

59% (00:54) correct 41% (01:02) wrong based on 101 sessions

HideShow timer Statistics

What is the sum of all common divisors of 48 and 36?

A. 22
B. 24
C. 26
D. 27
E. 28

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 51123

Show Tags

15 Sep 2014, 23:50
2
Official Solution:

What is the sum of all common divisors of 48 and 36?

A. 22
B. 24
C. 26
D. 27
E. 28

The common divisors of 48 and 36 are: 1, 2, 3, 4, 6, 12. Their sum is 28.

_________________
Intern
Joined: 13 Dec 2015
Posts: 4

Show Tags

05 Sep 2016, 19:13
Hello, what is the shortest working out steps to find the common divisor?
Intern
Joined: 07 Feb 2016
Posts: 21
GMAT 1: 650 Q47 V34
GMAT 2: 710 Q48 V39

Show Tags

07 May 2017, 00:39
unleesooj wrote:
Hello, what is the shortest working out steps to find the common divisor?

I did prime factorization in order to calculate the number of factors:

$$48=2^4*3^1$$

$$factors=5*2=10$$

and then divided 48 by ascending numbers:
$$48/1$$
$$48/2$$
$$48/3$$
$$48/4$$
$$...$$

This took me 2:15 for this question. Nevertheless, the very first step is not necessary, it was helping me not to forget any factor.
Manager
Joined: 14 May 2015
Posts: 51

Show Tags

07 May 2017, 02:17
36=1,2,3,4,6,9,12,18,36
48=1,2,3,4,6,8,12,16,24,48
common sum=1+2+3+4+6+12=28
ans: E
Intern
Joined: 04 Apr 2017
Posts: 17

Show Tags

16 Jun 2017, 10:59
1. Find the GCD of the numbers
2. Factors of GCD are also factors of the two numbers -> List out all the factors of the GCD.
3. Sum them up.
Intern
Joined: 13 Jun 2015
Posts: 9

Show Tags

23 Aug 2018, 05:36
Quote:
1. Find the GCD of the numbers
2. Factors of GCD are also factors of the two numbers -> List out all the factors of the GCD.
3. Sum them up.

Bunuel
Could you please confirm whether the above method should hold true for general cases? IMO the GCD should have all the common factors of a list of numbers. And there is that general formula to calculate the sum of all factors of a number, using which we can calculate the sum of factors of GCD. This should ideally provide a generic method to arrive at the sum of common factors for all numbers?
Please correct me if I am mistaken.

Thanks
Math Expert
Joined: 02 Sep 2009
Posts: 51123

Show Tags

23 Aug 2018, 21:52
1
shubhajit wrote:
Quote:
1. Find the GCD of the numbers
2. Factors of GCD are also factors of the two numbers -> List out all the factors of the GCD.
3. Sum them up.

Bunuel
Could you please confirm whether the above method should hold true for general cases? IMO the GCD should have all the common factors of a list of numbers. And there is that general formula to calculate the sum of all factors of a number, using which we can calculate the sum of factors of GCD. This should ideally provide a generic method to arrive at the sum of common factors for all numbers?
Please correct me if I am mistaken.

Thanks

_____________________________
Yes, that approach is generally true.
_________________
Manager
Joined: 21 Jun 2017
Posts: 156
Concentration: Finance, Economics
WE: Corporate Finance (Commercial Banking)

Show Tags

17 Nov 2018, 01:09
Hi guys,
Any shorter way to do this. This took me 3.5+ minutes. listed down all factors by brute force

_________________

Even if it takes me 30 attempts, I am determined enough to score 740+ in my 31st attempt. This is it, this is what I have been waiting for, now is the time to get up and fight, for my life is 100% my responsibility.

Manager
Joined: 28 Jun 2018
Posts: 67
GMAT 1: 490 Q39 V18
GMAT 2: 640 Q47 V30
GMAT 3: 670 Q50 V31
GMAT 4: 700 Q49 V36
GPA: 4

Show Tags

18 Nov 2018, 03:24
ShankSouljaBoi wrote:
Hi guys,
Any shorter way to do this. This took me 3.5+ minutes. listed down all factors by brute force

Hi,

1.Write down prime factorization of both numbers.

$$48 = 3 * 2^4$$
$$36 = 3^2 * 2^2$$

2. Next find GCD of the numbers.
GCD $$= 3 * 2^2$$ (To find GCD just write down the common prime factors. Then choose their lowest powers.)

3.Write down all the numbers u can make from this factorization.
$$1, 2, 3, 3*2 , 3*2*2 , 2*2$$
Sum them up! And you have the answer. This can be done within 2 minutes easily if u just be careful and practice step 3!

Hope it helps!
M14-04 &nbs [#permalink] 18 Nov 2018, 03:24
Display posts from previous: Sort by

M14-04

Moderators: chetan2u, Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.