It is currently 19 Sep 2020, 13:08

### 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

# (3x - 7y)^2

Author Message
TAGS:
Founder
Joined: 18 Apr 2015
Posts: 13305
Followers: 286

Kudos [?]: 3369 [0], given: 12171

(3x - 7y)^2 [#permalink]  05 Nov 2017, 01:12
Expert's post
00:00

Question Stats:

91% (00:21) correct 8% (00:20) wrong based on 71 sessions

 Quantity A Quantity B $$(3x - 7y)^2$$ $$9x^2 - 42xy + 49y^2$$

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________

Need Practice? 20 Free GRE Quant Tests available for free with 20 Kudos
GRE Prep Club Members of the Month: Each member of the month will get three months free access of GRE Prep Club tests.

Director
Joined: 03 Sep 2017
Posts: 518
Followers: 2

Kudos [?]: 432 [1] , given: 66

Re: (3x - 7y)^2 [#permalink]  05 Nov 2017, 02:55
1
KUDOS
Quantity A is the square of a binomial that is computed as $$(a-b)^2 = a^2-2ab+b^2$$. Thus, applying the formula to our case, we get exactly the same quantity of B.

Manager
Joined: 22 Feb 2018
Posts: 163
Followers: 2

Kudos [?]: 138 [1] , given: 22

Re: (3x - 7y)^2 [#permalink]  28 Mar 2018, 15:01
1
KUDOS
(3x - 7y)^2 = (3x)^2 + (7y)^2 - 2*3x*(-7y) = 9x^2 + 49y^2 - 42xy
These two are equal.

_________________

Intern
Joined: 23 Nov 2017
Posts: 45
Followers: 0

Kudos [?]: 53 [1] , given: 0

Re: (3x - 7y)^2 [#permalink]  29 Mar 2018, 13:42
1
KUDOS
Carcass wrote:

 Quantity A Quantity B $$(3x - 7y)^2$$ $$9x^2 - 42xy + 49y^2$$

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.

Ideally you should use the foil method but since time is an issue with the GRE you should probably just cheat and take a shortcut.

9x^2 - 42xy + 49y^2 is a perfect trinomial so we can use a special formula to simplify it into a binomial.

The first term will be the square root of the trinomial's first term (9x^2) which is 3x.
The second term will be the suare root of the trinomials term term (49y^2) which is 7y.
A negative sign with a positive sign gets us a negative sign.

Our binomial is hence 3x-7y.

Notice that if you multiply 3x by -7y you will get -21xy which is half of -42xy.

Manager
Joined: 29 Nov 2017
Posts: 190
Location: United States
GRE 1: Q142 V146
WE: Information Technology (Computer Software)
Followers: 1

Kudos [?]: 93 [0], given: 99

Re: (3x - 7y)^2 [#permalink]  16 May 2018, 03:33
Will it be a wrong approach to plug in different values of X and Y and land on the option D.

however, certainly the answer can be found by expanding the formula.
Retired Moderator
Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 171

Kudos [?]: 2914 [2] , given: 394

Re: (3x - 7y)^2 [#permalink]  16 May 2018, 04:07
2
KUDOS
Expert's post
IshanGre wrote:
Will it be a wrong approach to plug in different values of X and Y and land on the option D.

however, certainly the answer can be found by expanding the formula.

Plugging values is a method of elemination. Ideally one should use it when other options are not available.

Also ideally pick questions where the number of variables is low. Otherwise the number of values you need totest your hypothesis becomes too large.

For example a question with one variable can be tested with 2 or 3 points

A question with 2 variables would need 4 or 9 points (2points * 2points (4) or 3 points * 3points (9)).

In this case best avoid plugging unless you have run out of options.
_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test

Manager
Joined: 29 Nov 2017
Posts: 190
Location: United States
GRE 1: Q142 V146
WE: Information Technology (Computer Software)
Followers: 1

Kudos [?]: 93 [0], given: 99

Re: (3x - 7y)^2 [#permalink]  17 May 2018, 21:44
sandy wrote:
IshanGre wrote:
Will it be a wrong approach to plug in different values of X and Y and land on the option D.

however, certainly the answer can be found by expanding the formula.

Plugging values is a method of elemination. Ideally one should use it when other options are not available.

Also ideally pick questions where the number of variables is low. Otherwise the number of values you need totest your hypothesis becomes too large.

For example a question with one variable can be tested with 2 or 3 points

A question with 2 variables would need 4 or 9 points (2points * 2points (4) or 3 points * 3points (9)).

In this case best avoid plugging unless you have run out of options.

Thats great advice!! thank you-- -I got your point , i'll plug in values when the variables numbers are low.
Manager
Joined: 09 Mar 2019
Posts: 52
Followers: 0

Kudos [?]: 15 [0], given: 0

Re: (3x - 7y)^2 [#permalink]  08 Jun 2019, 10:15
Man this is not a harder question at all, please move it to the easier one.
THANKS.
Founder
Joined: 18 Apr 2015
Posts: 13305
Followers: 286

Kudos [?]: 3369 [0], given: 12171

Re: (3x - 7y)^2 [#permalink]  08 Jun 2019, 10:18
Expert's post
I didn't put the tag there. Usually, when I post a question I checked it out on my own.

Rarely, I put the wrong tag. For sure not hard when is easy. Moreover, more often than not is the same book that targets that question as easy,medium, hard, very hard

Thanks
_________________

Need Practice? 20 Free GRE Quant Tests available for free with 20 Kudos
GRE Prep Club Members of the Month: Each member of the month will get three months free access of GRE Prep Club tests.

Re: (3x - 7y)^2   [#permalink] 08 Jun 2019, 10:18
Display posts from previous: Sort by