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

It is currently 12 Dec 2018, 17:51

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.

Close

Request Expert Reply

Confirm Cancel
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.

What is the square root of 239,121?

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

Hide Tags

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51121
What is the square root of 239,121?  [#permalink]

Show Tags

New post 16 Apr 2015, 03:55
3
6
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

70% (00:46) correct 30% (00:46) wrong based on 340 sessions

HideShow timer Statistics

Most Helpful Community Reply
Intern
Intern
avatar
Joined: 31 Jan 2015
Posts: 2
GMAT 1: 720 Q48 V41
GPA: 3.65
Premium Member Reviews Badge
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 16 Apr 2015, 07:14
4
3
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


According to divisibility rules, 239,121 is divisible by 9.

2+3+9+1+2+1=18

This means, that the answer choice must be divisible by 3

A) 4+7+6= 17 NO
B) 4+8+9= 21 YES
C) 4+9+7= 20 NO
D) 5+1+1= 7 NO
E) 5+2+4= 11 NO

B is the only answer that can work.
General Discussion
Retired Moderator
avatar
B
Status: On a mountain of skulls, in the castle of pain, I sit on a throne of blood.
Joined: 30 Jul 2013
Posts: 327
GMAT ToolKit User Reviews Badge
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 16 Apr 2015, 04:01
1
4
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.

A, C and E out as the square of its last digit 6,7 and 4 is 6, 9 and 6 respectively.

\(500^2\)=250,000
So the square will be less than 500. So D is out as 511>500

B is the only possible answer.
Senior Manager
Senior Manager
User avatar
B
Joined: 28 Feb 2014
Posts: 294
Location: United States
Concentration: Strategy, General Management
Reviews Badge
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 16 Apr 2015, 09:11
1
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


I only looked at the last digit of 239121
only the last digits of B and D when squared will result in a 1 for the last digit.
500 squared is 250000 so D is out

Answer : B
Current Student
User avatar
B
Joined: 25 Nov 2014
Posts: 99
Concentration: Entrepreneurship, Technology
GMAT 1: 680 Q47 V38
GPA: 4
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 16 Apr 2015, 10:14
1
1
1) Checking the last digits in the answer options A, C, E are out since last digit of the square is known to be 1.
2) B = 489^2 and D = 511^2
B = (500-11)^2 and D = (500 + 11)^2

Since we need the answer less than 250000 => D is out.
Thus we have B as the ans.
_________________

Kudos!!

Manager
Manager
avatar
Joined: 15 May 2014
Posts: 62
GMAT ToolKit User Premium Member
What is the square root of 239,121?  [#permalink]

Show Tags

New post 18 Apr 2015, 00:29
1
Square root of\(\,\,\,\,239,121\)

Finding Last digit:
if unit's digit of Square is 1,
then possible unit's digit of Square Root is either 1 or 9

Finding First Digit:
Split the Square into groups of TWO digits from RIGHT TO LEFT
(if the extreme left group has only one number then it's also a group)
\(23\,\,91\,\,21\)
\(perfect\,square\,\leq\,first\,group\)
\(4^2\,\leq\,23\)

So answer should have \(4\) as the first digit and \(1\,or\,9\) as the last digit

Answer B
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51121
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 20 Apr 2015, 04:46
2
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION

The square root of 239,121 represents the number that, squared, will give you 239,121. With a calculator this problem is plug-and-play, and at most it will take 45 seconds to try all five combinations and see which answer is correct. Without a calculator to do all the heavy lifting, we have to get a little smarter.

The brute force approach will still work. Simply multiply 476 by 476 and find the product. If it is not 239,121, we rinse and repeat for all five numbers. This technique does work, but it will take a significant amount of time as it ignores the hints the exam is giving you to solve the question quickly.

A great concept to utilize here is the idea of the unit digit. If I multiply any two numbers, the unit digit will simply be the product of the unit digits of the two numbers. This is because there is no carry over from other positions possible. Hence, here we need a number that gives a unit digit of 1 when we multiply it by itself. Going through each option, we can eliminate A (6×6), C (7×7) and E (4×4). This should make a lot of intuitive sense because any even number multiplied by itself will give you another even number, so answers A and E were never in the running. Answer choice C could have worked, but 7×7 must yield a unit digit of 9, so it cannot possibly work.

Only two answer choices remain: 489 and 511. Unfortunately, they both give unit digits of 1, so we need a different strategy to determine which answer is correct. This is where the concept of order of magnitude can save us the trouble of actually having to calculate the numbers. It’s worth noting that at this point multiplying one of the numbers will either give the correct answer or the incorrect answer. Either option solves the question, and is a legitimate way of getting the correct answer. However, knowing that 5 x 5 gives 25 means that 500 x 500 must give 25 followed by four 0’s, or 250,000. Since our number is a little below that, we know the answer must be smaller than 500, but not by very much. Answer choice D is thus too big to be the correct answer, and answer choice B must be correct.

There are many questions like this one that can be solved without having to do any math whatsoever, simply by knowing how to apply mathematical properties. This is what makes the GMAT tricky. The questions will not ask for very difficult math to be executed, but figuring out the correct way to get the correct answer is never a question of blindly attacking the problem with a brute force approach. This is why there is a timing component on the GMAT: To avoid reliance on brute forcing the answer (also to allow multiple tests to be scheduled in the same day). Focusing your study approach on the how, rather than the what, will help you maximize your score.

An apropos comparison is to think of the GMAT as an industrial strength lock. If you try to force your way in, the resistance will be significant. However if you know the combination to the lock, it will open easily. The key (pun intended) is to ascertain how to approach each question and work on the skillful approach instead of the forceful approach. Best of all, inside the safe is a ticket to the business school of your choice. Your job is to find the best way inside the safe. The lock mechanism is designed to keep you out, but like a password that is just “password”, it only appears difficult until you crack the safe.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Manager
Manager
User avatar
Joined: 23 Sep 2015
Posts: 83
Concentration: General Management, Finance
GMAT 1: 680 Q46 V38
GMAT 2: 690 Q47 V38
GPA: 3.5
What is the square root of 239,121?  [#permalink]

Show Tags

New post Updated on: 05 Nov 2015, 22:58
guess I missed something! sorry don't follow this method! lol

Originally posted by GMATDemiGod on 05 Nov 2015, 21:54.
Last edited by GMATDemiGod on 05 Nov 2015, 22:58, edited 1 time in total.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51121
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 05 Nov 2015, 21:56
Veritas Prep GMAT Instructor
User avatar
B
Joined: 15 Jul 2015
Posts: 110
GPA: 3.62
WE: Corporate Finance (Consulting)
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 06 Nov 2015, 07:05
2
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


All of the answers are around 500. Since this is an easy number to square, checking it first (500 x 500 = 250,000) reveals that the correct answer must be less than 500. Thus, we can eliminate D and E right off the bat. Next, since the units digit of the product is 1, we need to determine which numbers give us a units digit of 1 when squaring. Only 1 and 9 do - so, the correct answer must be B.
_________________

Dennis
Veritas Prep | GMAT Instructor

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Target Test Prep Representative
User avatar
P
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 4294
Location: United States (CA)
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 06 Jan 2017, 09:58
Bunuel wrote:
What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


When calculating the square root of 239,121, we must remember that we are looking for a number such that when it’s multiplied by itself (or squared) it produces a units digit of 1 (since 239,121 has a units digit of 1).

Of our answer choices, the only two numbers that will produce a units digit of 1, when squared, are 489 and 511.

However, because 500^2 = 250,000, we see that 511^2 > 250,000, whereas 489^2 < 250,000. Thus, the square root of 239,121 must equal 489.

Answer: B
_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Manager
Manager
User avatar
S
Joined: 30 May 2018
Posts: 85
Concentration: General Management, Marketing
GMAT 1: 750 Q49 V45
GPA: 3.45
WE: Other (Retail)
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 01 Oct 2018, 04:52
Square of 500 = 250000 which is more than 239121 , hence option D & E are incorrect.
out of options A,B and C - Only option B has 9 as units digits hence ensuring that a square of the same will end in 1 - leaves us with B as the only answer option !
Time taken : 15 seconds.
_________________

Kudos if you agree , Comment if you don't !!!

Manager
Manager
avatar
B
Joined: 16 Jun 2018
Posts: 54
Re: What is the square root of 239,121?  [#permalink]

Show Tags

New post 02 Oct 2018, 22:52
Bunuel wrote:

What is the square root of 239,121?

(A) 476
(B) 489
(C) 497
(D) 511
(E) 524

Kudos for a correct solution.


Since the unit digit is 1, therefore the square root of 239,121 must have either 9 or 1.

Now, we can eliminate options A, C and E. Of the remaining, B and D, options the nearest number is 500, whose square in 2500. Since our number in question stem is less than 2500. Therefore option B is the answer.

Please comment whether my reasoning is correct and whether my grammar is fine too .

Thanks
GMAT Club Bot
Re: What is the square root of 239,121? &nbs [#permalink] 02 Oct 2018, 22:52
Display posts from previous: Sort by

What is the square root of 239,121?

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


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

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®.