Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 25 May 2017, 02:02

### 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 June
Open Detailed Calendar

# If x and y are positive integers such that the product of x

Author Message
Manager
Joined: 25 Feb 2008
Posts: 53
Followers: 0

Kudos [?]: 14 [0], given: 0

If x and y are positive integers such that the product of x [#permalink]

### Show Tags

23 Jul 2008, 07:22
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If x and y are positive integers such that the product of x and y is prime, what is the units’ digit of 7x + 9y?

(1) 24 < y < 32
(2) x = 1

(A) Statement (1) ALONE is sufficient to answer the question, but statement (2) alone is not.
(B) Statement (2) ALONE is sufficient to answer the question, but statement (1) alone is not.
(C) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient.
(D) EACH statement ALONE is sufficient to answer the question.
(E) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient
Senior Manager
Joined: 06 Apr 2008
Posts: 437
Followers: 1

Kudos [?]: 155 [0], given: 1

### Show Tags

23 Jul 2008, 07:37
Capthan wrote:
If x and y are positive integers such that the product of x and y is prime, what is the units’ digit of 7x + 9y?

(1) 24 < y < 32
(2) x = 1

(A) Statement (1) ALONE is sufficient to answer the question, but statement (2) alone is not.
(B) Statement (2) ALONE is sufficient to answer the question, but statement (1) alone is not.
(C) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient.
(D) EACH statement ALONE is sufficient to answer the question.
(E) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient

Product of two numbers prime means that one number is 1 and other number is prime number itself

Statement 1) tells that y is prime number since it is not 1 and prime number will be 29 in this case. Therefore 7x + 9y = 7*1 + 9*29. Sufficient

Statement 2) is not sufficient since it does not tell any way of finding value of y.

Current Student
Joined: 31 Aug 2007
Posts: 369
Followers: 1

Kudos [?]: 143 [0], given: 1

### Show Tags

23 Jul 2008, 08:09
nmohindru wrote:
Capthan wrote:
If x and y are positive integers such that the product of x and y is prime, what is the units’ digit of 7x + 9y?

(1) 24 < y < 32
(2) x = 1

(A) Statement (1) ALONE is sufficient to answer the question, but statement (2) alone is not.
(B) Statement (2) ALONE is sufficient to answer the question, but statement (1) alone is not.
(C) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient.
(D) EACH statement ALONE is sufficient to answer the question.
(E) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient

Product of two numbers prime means that one number is 1 and other number is prime number itself

Statement 1) tells that y is prime number since it is not 1 and prime number will be 29 in this case. Therefore 7x + 9y = 7*1 + 9*29. Sufficient

Statement 2) is not sufficient since it does not tell any way of finding value of y.

E, y could be 29 or 31.
Director
Joined: 23 Sep 2007
Posts: 787
Followers: 5

Kudos [?]: 192 [0], given: 0

### Show Tags

23 Jul 2008, 08:31
A

y = 31 or 29

the unit digit of 9y is going to be 1 for both cases

7 + 1 = 8
Current Student
Joined: 31 Aug 2007
Posts: 369
Followers: 1

Kudos [?]: 143 [0], given: 1

### Show Tags

23 Jul 2008, 08:54
gmatnub wrote:
A

y = 31 or 29

the unit digit of 9y is going to be 1 for both cases

7 + 1 = 8

Oops!
Retired Moderator
Joined: 18 Jul 2008
Posts: 975
Followers: 10

Kudos [?]: 219 [0], given: 5

### Show Tags

23 Jul 2008, 16:15
31 x 9 = 279
29 x 9 = 261

Did I miss something?

young_gun wrote:
gmatnub wrote:
A

y = 31 or 29

the unit digit of 9y is going to be 1 for both cases

7 + 1 = 8

Oops!
Senior Manager
Joined: 19 Mar 2008
Posts: 352
Followers: 1

Kudos [?]: 62 [0], given: 0

### Show Tags

25 Jul 2008, 07:50
xy= prime
one of x or y is 1 and the other is prime

(1) 24 < y < 32
so y is not 1
y can be 29 or 31
Not sufficient

(2) x = 1
no information on y
Not sufficient

(1) & (2)
we cannot get the exact info on y
not sufficient
Manager
Joined: 28 Apr 2008
Posts: 110
Followers: 1

Kudos [?]: 12 [0], given: 0

### Show Tags

26 Jul 2008, 03:52
E

from 1 and from the combination of 1 and 2 we know:
y could be 29 or 31

7*x=7

9*y= 9*31 or 9*29

the unit digit would therefore be 9 or 1

9+7=16, so unit 6

1+7=8, so unit 8

so ins
Re: Units' digit   [#permalink] 26 Jul 2008, 03:52
Display posts from previous: Sort by