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

 It is currently 15 Dec 2018, 08:08

### 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
• ### \$450 Tuition Credit & Official CAT Packs FREE

December 15, 2018

December 15, 2018

10:00 PM PST

11:00 PM PST

Get the complete Official GMAT Exam Pack collection worth \$100 with the 3 Month Pack (\$299)
• ### FREE Quant Workshop by e-GMAT!

December 16, 2018

December 16, 2018

07:00 AM PST

09:00 AM PST

Get personalized insights on how to achieve your Target Quant Score.

# An integer grater than 1 that is not prime is called

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 13 Oct 2016
Posts: 367
GPA: 3.98

### Show Tags

01 Jan 2017, 06:38
baalok88 wrote:
An integer greater than 1 that is not prime is called composite. If the two-digit integer is greater than 20, is n composite?

1. The tens digit of n is a factor of the units digit of n
2. The tens digit of n is 2

Here's How I followed it-
the integer will be 10y + x.
As per statement 1:
x is multiple of y i.e. for 24: x=4, y=2, OR for 26 : x =6, y=2

Hence Insufficient.

Statement 2: Insufficient.

Combining both also gives the ambiguity of the integer being 24 or 26.

Hence 'E'

Can you tell me what's the blunder I have made?

Hi

The question does not ask you to find exact value of the number. It just asks you "is the number composite or not?".

If tens digit is a factor of the units diit. That's insufficient because the tens digit can be 1 and units digi 7 (1 is also a factor of 7) and our number will be 17 - prime. Or tens digit can be 2 and our number 26 - composite.

But when we combine both 1 and 2 we get tens digit is 2 and units digit is 2x. We can factor out our 2 and th number will be omposite. In your example 24 = 2*12 or 26 = 2*13. Both composite. Sufficient.

Hope it's clear.
Intern
Joined: 12 Nov 2014
Posts: 6
Re: An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

01 Jan 2017, 20:47
vitaliyGMAT wrote:
baalok88 wrote:
An integer greater than 1 that is not prime is called composite. If the two-digit integer is greater than 20, is n composite?

1. The tens digit of n is a factor of the units digit of n
2. The tens digit of n is 2

Here's How I followed it-
the integer will be 10y + x.
As per statement 1:
x is multiple of y i.e. for 24: x=4, y=2, OR for 26 : x =6, y=2

Hence Insufficient.

Statement 2: Insufficient.

Combining both also gives the ambiguity of the integer being 24 or 26.

Hence 'E'

Can you tell me what's the blunder I have made?

Hi

The question does not ask you to find exact value of the number. It just asks you "is the number composite or not?".

If tens digit is a factor of the units diit. That's insufficient because the tens digit can be 1 and units digi 7 (1 is also a factor of 7) and our number will be 17 - prime. Or tens digit can be 2 and our number 26 - composite.

But when we combine both 1 and 2 we get tens digit is 2 and units digit is 2x. We can factor out our 2 and th number will be omposite. In your example 24 = 2*12 or 26 = 2*13. Both composite. Sufficient.

Hope it's clear.

Hi,
Should be A as the number can be any 24 26 28 , and n>20.. Please correct me if i am wrong
Intern
Joined: 25 Nov 2016
Posts: 10
Re: An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

01 Jan 2017, 21:40
As its mentioned in the question that numbers above 20
Intern
Joined: 27 Oct 2015
Posts: 5
An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

06 Jan 2017, 04:52
Please explain, why can't we consider 31( or 41) number for statement 1.

Is 3 a factor of 1?
Math Expert
Joined: 02 Sep 2009
Posts: 51218
Re: An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

06 Jan 2017, 05:16
20043856 wrote:
Please explain, why can't we consider 31( or 41) number for statement 1.

Is 3 a factor of 1?

In 31, 3 is the tens digit and 1 is the units digit. (1) says that the tens digit of n is a factor of the units digit of n but 3 is NOT a factor of 1, 1 is a factor of 3, or in another way 3 is a multiple of 1.

Hope it's clear.
_________________
Director
Joined: 26 Oct 2016
Posts: 640
Location: United States
Schools: HBS '19
GMAT 1: 770 Q51 V44
GPA: 4
WE: Education (Education)
Re: An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

29 Jan 2017, 17:21
For condition one - They have mentioned that ten's digit is a factor of one's digit.
Implying that numbers are - 22 ( 2 is factor of 2 ) , 24 ( 2 is a factor of 4 ) , 26, 28, 33, 36, 39 etc. Thus these numbers are composite as they are not prime.

Condition 2 , gives us 21,22,23,24....29. Of which 23, 29 are prime . Thus insufficient.

IMO - A .
_________________

Thanks & Regards,
Anaira Mitch

Manager
Joined: 31 Dec 2016
Posts: 73
An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

30 Jul 2017, 11:46
gmatmba wrote:
X & Y wrote:
An integer grater than 1 that is not prime is called composite. If the two-digit integer n is greater than 20, is n composite?

(1) The tens digit of n is a factor of the units digit of n.

(2) The tens digit of n is 2

Plz Explain..

(1) 24 (2 is a factor of 4), 39 (3 is a factor of 9), 48 (4 is a factor of 8) ... sufficient

(2) 22 composite, 23 not composite - not sufficient

This isn't a good way to do it because really you should be looking at primes and not composites. If one prime had a factor where the tens digit was a factor of its units then your answer is destroyed. All you did was prove that composites have some tens digits which are factors of units digits--it is impossible above 5 really for the tens to be a factor of the units because 6 doesn't go into 1,2,3,4,5,7,8,9. And we know 66,77,88 and 99 aren't prime as they have factors of 11 .
(1) It's better to list the prime. The prime between 20-60--you should memorize. Are: 23,29,31,37,41,43,49,53,59 and 61. Notice how none of the Tens are factors of the units number. So we know for a prime that the tens digit is not a factor of the units digit. For a composite we can have one example 22, in which we see the tens is a factor of the units. (2 is a factor of 2). So we can see primes don't have tens that are factors of units between 20-100 and composites can. Therefore it is not a prime and therefore is a composite

(2) If the 10's digit is 2, the number could be 22 or 23. NS

Non-Human User
Joined: 09 Sep 2013
Posts: 9164
Re: An integer grater than 1 that is not prime is called  [#permalink]

### Show Tags

12 Aug 2018, 04:25
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: An integer grater than 1 that is not prime is called &nbs [#permalink] 12 Aug 2018, 04:25

Go to page   Previous    1   2   [ 28 posts ]

Display posts from previous: Sort by