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

It is currently 18 Jul 2018, 21:06

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

The average (arithmetic mean) of y numbers is x. If 30 is added to the

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

Hide Tags

Expert Post
1 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 47086
The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 03:32
1
1
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

83% (01:13) correct 17% (01:35) wrong based on 84 sessions

HideShow timer Statistics

The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?

A. x/6 - 6
B. x/6 - 5
C. x/7 - 5
D. x/5 - 7
E. x/5 - 6

_________________

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

1 KUDOS received
Senior Manager
Senior Manager
User avatar
P
Joined: 02 Jul 2017
Posts: 294
GMAT 1: 730 Q50 V38
GMAT ToolKit User
Re: The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 03:56
1
Let sum of y numbers by S(y)

\(So Average = \frac{S(y)}{y}= x => S(y) = x*y\)

Now 30 is added to the list.
=> Sum = S(y)+30
No. of terms = y+1

\(So average = \frac{S(y) +30}{y+1}= x-5\)
=> S(y)+30 = (x-5)(y+1)
=> xy+30 = xy+x-5y-5
=> x-5y=35
=>5y=x-35
=>\(y= \frac{x}{5} -7\)

Answer: D
Manager
Manager
User avatar
S
Joined: 25 Jul 2011
Posts: 53
Location: India
Concentration: Strategy, Operations
GMAT 1: 740 Q49 V41
GPA: 3.5
WE: Engineering (Energy and Utilities)
Re: The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 03:57
Bunuel wrote:
The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?

A. x/6 - 6
B. x/6 - 5
C. x/7 - 5
D. x/5 - 7
E. x/5 - 6


Since mean of "y" numbers is "x"...sum of these no. = mean (or average)* number of nos=x*y
again..if a no 30 is added..sum will be (xy+30) and no of numbers will be y+1;

reapplying same formula... (xy+30)=(x-5)(y+1) as new mean is (x-5) as per question stem;

so...solving we get (xy+30)=xy+x-5y-5
35=x-5y
5y=x-35
or y=x/5-7 hence (D)

hit kudos if this was helpful :-)

_________________

Please hit kudos button below if you found my post helpful..TIA

Expert Post
Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 6238
Re: The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 04:03
Bunuel wrote:
The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?

A. x/6 - 6
B. x/6 - 5
C. x/7 - 5
D. x/5 - 7
E. x/5 - 6



AVG of y Numbers is x, so SUM is yx..
Add 30 to it yx+30..
So new avg = \(\frac{yx+30}{1+y}=x-5.....yx+30=x-5+xy-5y.....35=x-5y......y=\frac{x-35}{5}=\frac{x}{5}-7\)

D
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


GMAT online Tutor

Manager
Manager
User avatar
B
Joined: 19 Jul 2017
Posts: 85
Location: India
Concentration: General Management, Strategy
GPA: 3.5
Re: The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 05:43
Bunuel wrote:
The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?

A. x/6 - 6
B. x/6 - 5
C. x/7 - 5
D. x/5 - 7
E. x/5 - 6


Sum =Average *Number
Sum of y numbers is xy
Sum of y+1= (x-5)*y+1

xy+30 =(x-5)*(y+1)
xy+30=xy-5y+x-5
30+5=x-5y
x=5(y+7);
y=x/5-7

So Ans:D
SC Moderator
avatar
D
Joined: 22 May 2016
Posts: 1829
Premium Member CAT Tests
The average (arithmetic mean) of y numbers is x. If 30 is added to the [#permalink]

Show Tags

New post 13 Sep 2017, 10:19
Bunuel wrote:
The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?

A. x/6 - 6
B. x/6 - 5
C. x/7 - 5
D. x/5 - 7
E. x/5 - 6

If the equation is hard to set up, a simple A*n = S table can help.

The key is that one occurrence of a numeric value added or subtracted to the set of numbers gets its own row; then add column "n" to get total number and column "S" to get total sum (averages CANNOT be added).

__A__|__n__|___S____|
__x__|__y__|___xy____|
_30__|__1__|___30___|
-------|_y+1_|_xy+30__|

The new average is (x - 5). That doesn't get written in the table anywhere. It's the RHS of the equation.

LHS = \(\frac{Total Sum}{Total
Number}\)

\(\frac{(xy + 30)}{(y+1)} = (x - 5)\)

\(xy + 30 = (x - 5)(y + 1)\)
\(xy + 30 = xy + x - 5y - 5\)
\(5y = x - 35\)

\(y = \frac{x}{5} - 7\)

ANSWER D
_________________

In the depths of winter, I finally learned
that within me there lay an invincible summer.

-- Albert Camus, "Return to Tipasa"

The average (arithmetic mean) of y numbers is x. If 30 is added to the   [#permalink] 13 Sep 2017, 10:19
Display posts from previous: Sort by

The average (arithmetic mean) of y numbers is x. If 30 is added to the

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

Events & Promotions

PREV
NEXT


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®.