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

 It is currently 22 Oct 2019, 19:24 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  Which of the following is NOT a difference between two perfect squares

 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: 58427
Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags 00:00

Difficulty:   55% (hard)

Question Stats: 52% (01:36) correct 48% (01:34) wrong based on 100 sessions

HideShow timer Statistics

Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

_________________
Marshall & McDonough Moderator D
Joined: 13 Apr 2015
Posts: 1683
Location: India
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

1
A. 3^2 - 2^2 = 5

B. 4^2 - 3^2 = 7

C. 3^2 - 1^2 = 8

D. 7^2 - 6^2 = 13

Posted from my mobile device
CEO  D
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2978
Location: India
GMAT: INSIGHT
Schools: Darden '21
WE: Education (Education)
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

1
Bunuel wrote:
Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

difference between two perfect squares = a^2 - b^2 = (a+b)*(a-b)

Hence the number which can not be represented in form of (a+b)*(a-b) form will be our answer

Also, every odd number can be represented in (a+b)*(a-b) form (as shown in calculation below) hence options A,B and E are straight out

A. 5 = 5*1 = (3+2)*(3-2)
B. 7 = 7*1 = (4+3)*(4-3)
C. 8 = 4*2 = (3+1)*(3-1)
D. 13 = 13*1 = (7+6)*(7-6)
E. 18 CAN'T be represented as (a+b)*(a-b) form

_________________
Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION
Target Test Prep Representative D
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 8129
Location: United States (CA)
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

Bunuel wrote:
Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

The first few perfect squares are 1^2 = 1, 2^2 = 4, 3^2 = 9, 4^2 = 16, 5^2 = 25, 6^2 = 36, and 7^2 = 49. Let’s test our answer choices:

A) 5

9 - 4 = 5

B) 7

16 - 9 = 7

C) 8

9 - 1 = 8

D) 13

49 - 36 = 13

E) 18

We see that 18 cannot be the difference between 2 perfect squares.

_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Math Expert V
Joined: 02 Aug 2009
Posts: 8008
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

Bunuel wrote:
Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

There is always logic in almost all Questions..

So what is the point here..
$$a^2-b^2=(a-b)(a+b)$$..
If a-b is even, a+b will be even and if a-b is odd, a+b will be odd...
So if a number cannot be written as O*O or E*E, that is our answer..
1) 5=1*5..o*o
2) 7=1*7..o*o
3) 8=2*4..E*E
4) 13= 1*13..o*o
5) 18=1*18=2*9=3*6...o*E.. thus our ANSWER..

E
_________________
Director  P
Joined: 31 Jul 2017
Posts: 512
Location: Malaysia
Schools: INSEAD Jan '19
GMAT 1: 700 Q50 V33 GPA: 3.95
WE: Consulting (Energy and Utilities)
Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

Bunuel wrote:
Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

Hi Bunuel

I think the question is missing something here.. because all the options are difference between two perfect square NUMBERS.

chetan2u Can you please let me know if I am missing anything here.

A. $$(a+b)(a-b) = (3+2)(3-2) = 5$$
B. $$(a+b)(a-b) = (4+3)(4-3) = 7$$
C. $$(a+b)(a-b) = (3+1)(3-1) = 8$$
D. $$(a+b)(a-b) = (7+6)(7-6) = 13$$
E. $$(a+b)(a-b) = (5\sqrt{2} + 4\sqrt{2})(5\sqrt{2}-4\sqrt{2}) = 18$$
_________________
If my Post helps you in Gaining Knowledge, Help me with KUDOS.. !!

Originally posted by rahul16singh28 on 31 Jan 2018, 20:08.
Last edited by rahul16singh28 on 01 Feb 2018, 00:08, edited 1 time in total.
Senior Manager  P
Joined: 07 Jul 2012
Posts: 366
Location: India
Concentration: Finance, Accounting
GPA: 3.5
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

$$(5\sqrt{2})^2$$= 50 [Not a perfect square]
$$(4\sqrt{2})^2$$= 32 [Not a perfect square]
_________________
Kindly hit kudos if my post helps!
Director  P
Joined: 31 Jul 2017
Posts: 512
Location: Malaysia
Schools: INSEAD Jan '19
GMAT 1: 700 Q50 V33 GPA: 3.95
WE: Consulting (Energy and Utilities)
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

varun4s wrote:
$$(5\sqrt{2})^2$$= 50 [Not a perfect square]
$$(4\sqrt{2})^2$$= 32 [Not a perfect square]

They are perfect squares.. 50 = (5√2)^2 and 32 = (4√2)^2... Also, it's not mentioned in the question that whether it's a integer or a Number.. !!

Sent from my Lenovo P1a42 using GMAT Club Forum mobile app
_________________
If my Post helps you in Gaining Knowledge, Help me with KUDOS.. !!
Math Expert V
Joined: 02 Sep 2009
Posts: 58427
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

1
rahul16singh28 wrote:
varun4s wrote:
$$(5\sqrt{2})^2$$= 50 [Not a perfect square]
$$(4\sqrt{2})^2$$= 32 [Not a perfect square]

They are perfect squares.. 50 = (5√2)^2 and 32 = (4√2)^2... Also, it's not mentioned in the question that whether it's a integer or a Number.. !!

Sent from my Lenovo P1a42 using GMAT Club Forum mobile app

A perfect square is a square of an integer.
_________________
Math Expert V
Joined: 02 Aug 2009
Posts: 8008
Re: Which of the following is NOT a difference between two perfect squares  [#permalink]

Show Tags

rahul16singh28 wrote:
Bunuel wrote:
Which of the following is NOT a difference between two perfect squares?

A. 5
B. 7
C. 8
D. 13
E. 18

Hi Bunuel

I think the question is missing something here.. because all the options are difference between two perfect square NUMBERS.

chetan2u Can you please let me know if I am missing anything here.

A. $$(a+b)(a-b) = (3+2)(3-2) = 5$$
B. $$(a+b)(a-b) = (4+3)(4-3) = 7$$
C. $$(a+b)(a-b) = (3+1)(3-1) = 8$$
D. $$(a+b)(a-b) = (7+6)(7-6) = 13$$
E. $$(a+b)(a-b) = (5\sqrt{2} + 4\sqrt{2})(5\sqrt{2}-4\sqrt{2}) = 18$$

Hi Rahul,
If we go by this EVERY number will be a perfect square..
But a perfect square means a square of an INTEGER
_________________ Re: Which of the following is NOT a difference between two perfect squares   [#permalink] 01 Feb 2018, 00:32
Display posts from previous: Sort by

Which of the following is NOT a difference between two perfect squares

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

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne  