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

It is currently 23 Jan 2019, 12:58

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 January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
  • Key Strategies to Master GMAT SC

     January 26, 2019

     January 26, 2019

     07:00 AM PST

     09:00 AM PST

    Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.
  • Free GMAT Number Properties Webinar

     January 27, 2019

     January 27, 2019

     07:00 AM PST

     09:00 AM PST

    Attend this webinar to learn a structured approach to solve 700+ Number Properties question in less than 2 minutes.

The average of two numbers is XY. If the first number is Y, what is

  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: 52431
The average of two numbers is XY. If the first number is Y, what is  [#permalink]

Show Tags

New post 28 Feb 2018, 23:35
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

81% (01:10) correct 19% (01:20) wrong based on 57 sessions

HideShow timer Statistics

Intern
Intern
avatar
B
Joined: 12 Nov 2017
Posts: 15
Re: The average of two numbers is XY. If the first number is Y, what is  [#permalink]

Show Tags

New post 28 Feb 2018, 23:41
(X+Y)/2 =X*Y =>X = 2XY-Y


Sent from my Redmi Note 4 using GMAT Club Forum mobile app
Senior SC Moderator
avatar
V
Joined: 22 May 2016
Posts: 2374
The average of two numbers is XY. If the first number is Y, what is  [#permalink]

Show Tags

New post 01 Mar 2018, 11:11
Bunuel wrote:
The average of two numbers is X*Y. If the first number is Y, what is the other number?

(A) 2XY-Y

(B) XY-2Y

(C) 2XY-X

(D) Z

(E) XY-Y

Algebra
Let the second number = Q

The average of two numbers is X*Y. The first number is Y.
\(\frac{Q+Y}{2} = XY\)
\(Q+Y = 2XY\) (Subtract Y)
\(Q = 2XY - Y\)


Answer A

Assign values
For this question, assigning values may not feel intuitive. Answer D, "Z," is a trap.

If we set up the equation with Z as "the other number," by definition, Z is the answer. That's circular reasoning. There is no "content" to the answer. What is Z's value? We have no idea.

All we need is the RHS of the equation once "other number" is isolated.

Let X = 1
Let Y = 2
Let other number = ?

\(\frac{(? + Y)}{2} = (X*Y)\)

\(\frac{(? + 2)}{2} = (1*2)\)

\(? + 2 = 2(2)\)
\(? = 4 - 2\)
\(? = 2\)


The other number (?) is 2
With X=1 and Y=2, find the answer choice that yields 2

(A) 2XY-Y: \((2(1*2) - 2) = (4 - 2) = 2.\) MATCH

(B) XY-2Y: \((1*2) - (2*2) = (2 - 4) = -2.\) NO

(C) 2XY-X: \((2*(1*2)) - 1) = (4 - 1) = 3.\) NO

(D) Z: we have no idea what Z equals. NO

(E) XY-Y: \(((1*2) - 2) = (2 - 2) = 0.\) NO

Answer A
_________________

Sometimes at night I would sleep open-eyed underneath a sky dripping with stars.
I was alive then.

—Albert Camus

Manager
Manager
avatar
S
Joined: 23 Sep 2016
Posts: 214
Premium Member Reviews Badge
Re: The average of two numbers is XY. If the first number is Y, what is  [#permalink]

Show Tags

New post 03 Mar 2018, 01:31
Bunuel wrote:
The average of two numbers is X*Y. If the first number is Y, what is the other number?

(A) 2XY-Y

(B) XY-2Y

(C) 2XY-X

(D) Z

(E) XY-Y

lets total be T
so average be T/2=xy
t=2xy
if 1st number is Y then second number is 2xy-y
CEO
CEO
User avatar
P
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2726
Location: India
GMAT: INSIGHT
Schools: Darden '21
WE: Education (Education)
Reviews Badge
Re: The average of two numbers is XY. If the first number is Y, what is  [#permalink]

Show Tags

New post 03 Mar 2018, 01:42
Bunuel wrote:
The average of two numbers is X*Y. If the first number is Y, what is the other number?

(A) 2XY-Y

(B) XY-2Y

(C) 2XY-X

(D) Z

(E) XY-Y


(a+Y)/2 = X*Y

i.e. a+Y = 2X*Y

i.e. a = 2X*Y - Y

Answer: Option A
_________________

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

GMAT Club Bot
Re: The average of two numbers is XY. If the first number is Y, what is &nbs [#permalink] 03 Mar 2018, 01:42
Display posts from previous: Sort by

The average of two numbers is XY. If the first number is Y, what is

  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®.