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

 It is currently 23 May 2019, 10:46 ### 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. ### Request Expert Reply # D represents a single digit number from 1 to 9. What is the value of D

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Math Expert V
Joined: 02 Sep 2009
Posts: 55266
D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags 00:00

Difficulty:   45% (medium)

Question Stats: 72% (01:53) correct 28% (02:11) wrong based on 246 sessions

### HideShow timer Statistics

D represents a single digit number from 1 to 9. What is the value of D?

(1) D.D + DD = D.D × DD
(2) D is not a prime number.

The dot (.) represents a decimal point.

_________________
Current Student P
Joined: 18 Aug 2016
Posts: 618
Concentration: Strategy, Technology
GMAT 1: 630 Q47 V29 GMAT 2: 740 Q51 V38 Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

1
Bunuel wrote:
D represents a single digit number from 1 to 9. What is the value of D?

(1) D.D + DD = D.D × DD
(2) D is not a prime number.

The dot (.) represents a decimal point.

(1) D.D + DD = D.D × DD
1.1 + 11 = 1.1 * 11 Yes
2.2 + 22 = 2.2 * 22 No

9.9 + 99 = 9.9 * 99 No (Only D=1 can hold)

Sufficient

(2) D can represent 2, 3, 5, 7...Not Sufficient

A
_________________
We must try to achieve the best within us

Thanks
Luckisnoexcuse
Intern  B
Joined: 21 Jun 2017
Posts: 10
GMAT 1: 750 Q50 V41 Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

(1)Sufficient
D +D/10 + 11D = (D+D/10)*11D
-> 121D = 121D^2
-> D(D-1) = 0
D is from 1-9 so D =1
(2) Not
D can be 1,4,6,8,9
Intern  B
Joined: 18 Aug 2017
Posts: 30
GMAT 1: 670 Q49 V33 Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

2
My approach:

1- Let 2 digit number DD is a, then D.D = a/10

a/10 + a = a/10 x a
11a/10 = a^2 /10
11 = a (a is positive so we can get rid of a/10 on both side)

so D = 1 => SUFF

2- D not prime, so D can be 4, 6, 8 => INSUFF

A is the answer.
Senior Manager  S
Joined: 15 Jan 2017
Posts: 351
Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

Tried plugging in, which worked:
1) 22*2.2 = 22+2.2 not possible
11*1.1 = 11+ 1.1 --> possible
Suff
2) D not prime -- multiple values possible then. Not suff

Ans A
EMPOWERgmat Instructor V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 14197
Location: United States (CA)
GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

Hi All,

This question can be solved with a little math and a bit of 'brute force.'

We're told that D is a positive DIGIT (meaning 1-9, inclusive). We're asked for the value of D.

1) D.D + DD = (D.D)(DD)

While this might look complex, if you substitute in a value for D, you'll find that math to be rather straight-forward....

IF.... D = 1, we have...
1.1 + 11 = (1.1)(11)

Does that equation 'balance out?'
1.1 + 11 = 12.1
(1.1)(11) = 12.1
So YES, D could equal 1.

What about D = 2? Does....
2.2 + 22 = (2.2)(22)

You should be able to answer that question WITHOUT actually doing the math. On the left side, you're ADDING 10% of 22 to 22 and on the right side you're MULTIPLYING those values. The right side will clearly be a lot bigger than the left side. This means that D CANNOT equal 2.

Now how about D=3? D=4? Etc. You should see that you run into the same issue that you did when we worked through D=2: the right side is much bigger than the left side, so there's really no need to check all of those values. This means that D=1 is the ONLY possible solution.
Fact 1 is SUFFICIENT.

2) D is not a prime number

This tells us that D cannot be 2, 3, 5 or 7.... but that still leaves us with 5 other possibilities (1, 4, 6, 8 and 9)
Fact 2 is INSUFFICIENT.

Final Answer:

GMAT assassins aren't born, they're made,
Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****

# Rich Cohen

Co-Founder & GMAT Assassin Follow
Special Offer: Save \$75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/
Intern  B
Joined: 10 Feb 2018
Posts: 5
Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

Bunuel wrote:
D represents a single digit number from 1 to 9. What is the value of D?

(1) D.D + DD = D.D × DD
(2) D is not a prime number.

The dot (.) represents a decimal point.

by statement 1,

D.D + DD = (D.D) (DD)
$$\frac{DD}{10}+ DD = \frac{DD}{10} (DD)$$
DD + 10DD = (DD) (DD)
11DD = (DD) (DD)
DD = 11

therefore, statement 1 is sufficient.

Statement 2 gives no proper information.

Therefore answer is A.

Please correct me if my solution is wrong.
Thanks
Intern  B
Joined: 24 Jan 2018
Posts: 1
Re: D represents a single digit number from 1 to 9. What is the value of D  [#permalink]

### Show Tags

(1) DD+D.D=DD*D.D
=DD(1+1/10)=(DD^2)/10
=11/10=DD/10
DD=11
SUFFICIENT

(2) D can represent 2, 3, 5, 7...NOT SUFFICIENT Re: D represents a single digit number from 1 to 9. What is the value of D   [#permalink] 08 Apr 2018, 09:44
Display posts from previous: Sort by

# D represents a single digit number from 1 to 9. What is the value of D

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics 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®.

#### MBA Resources  