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

It is currently 14 Dec 2018, 12:25

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
  • Typical Day of a UCLA MBA Student - Recording of Webinar with UCLA Adcom and Student

     December 14, 2018

     December 14, 2018

     10:00 PM PST

     11:00 PM PST

    Carolyn and Brett - nicely explained what is the typical day of a UCLA student. I am posting below recording of the webinar for those who could't attend this session.
  • Free GMAT Strategy Webinar

     December 15, 2018

     December 15, 2018

     07:00 AM PST

     09:00 AM PST

    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

The average age of a group of n people is 15 yrs. One more person aged

  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: 51215
The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 19 Aug 2015, 01:01
1
6
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

84% (00:55) correct 16% (01:05) wrong based on 189 sessions

HideShow timer Statistics

The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13

Kudos for a correct solution.

_________________

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

Senior Manager
Senior Manager
User avatar
S
Joined: 21 Jan 2015
Posts: 355
Location: India
Concentration: Strategy, Marketing
GMAT 1: 620 Q48 V28
GMAT 2: 690 Q49 V35
WE: Sales (Consumer Products)
GMAT ToolKit User CAT Tests
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 19 Aug 2015, 02:06
1
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13



Ans: C

Solution: (15n+39)/(n+1) = 17
this gives us n=11
_________________

--------------------------------------------------------------------
The Mind is Everything, What we Think we Become.

Manager
Manager
User avatar
Joined: 10 Jun 2015
Posts: 118
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 19 Aug 2015, 02:19
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13

Kudos for a correct solution.


Total age of n people = 15n
(15n+39)/(n+1)=17, given
solving, we get n=11
The correct option is C
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51215
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 23 Aug 2015, 11:41
1
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION:

First tell me, if the age of the additional person were 15 yrs, what would have happened to the average? The average would have remained the same since this new person’s age would have been the same as the age that represents the group. But his age is 39 – 15 = 24 more than the average. We know that we need to evenly split the extra among all the people to get the new average. When 24 is split evenly among all the people (including the new guy), everyone gets 2 extra (since average age increased from 15 to 17). There must be 24/2 = 12 people now (including the new guy) i.e. n must be 11 (without including the new guy).
_________________

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

Current Student
User avatar
D
Joined: 12 Aug 2015
Posts: 2627
Schools: Boston U '20 (M)
GRE 1: Q169 V154
GMAT ToolKit User Premium Member
The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 08 Dec 2016, 23:27
1
Great Question.
Here is my solution to this one =>

This can be solved via two ways:-

Method 1-->
Using the Formula =>
\(Mean =\frac{Sum}{#}\)

\(Sum =15n\)
\(\frac{15n+39}{n+1} => 17\)
Hence \(2n=22\)
\(n=11\)


Method 2-->
Here Old mean =15
New mean =17
hence 2 is getting added to each n+1 terms.
Now difference between 15 and 39 is 24
hence 2(n+1)=24
So.n=11

Hence C

_________________


MBA Financing:- INDIAN PUBLIC BANKS vs PRODIGY FINANCE!

Getting into HOLLYWOOD with an MBA!

The MOST AFFORDABLE MBA programs!

STONECOLD's BRUTAL Mock Tests for GMAT-Quant(700+)

AVERAGE GRE Scores At The Top Business Schools!

CEO
CEO
User avatar
D
Joined: 11 Sep 2015
Posts: 3237
Location: Canada
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 12 Oct 2018, 12:41
Top Contributor
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13

Kudos for a correct solution.


The average age of a group of n people is 15 yrs.
So, (sum of all n ages)/n = 15
Multiply both sides by n to get: (sum of all n ages) = 15n

One more person aged 39 joins the group and the new average is 17 yrs.
IMPORTANT: Once this 39-year-old is added to the group, the (NEW sum of ages) = 15n + 39 [We just added 39 to the old sum]
Since we now have n+1 people, we can write: (15n + 39)/(n + 1) = 17
Multiply both sides by n to get: 15n + 39 = 17(n + 1)
Expand right side: 15n + 39 = 17n + 17
Subtract 15n from both sides to get: 39 = 2n + 17
Subtract 17 from both sides to get: 22 = 4n
Solve: n = 11

Answer: C

RELATED VIDEO FROM OUR COURSE

_________________

Test confidently with gmatprepnow.com
Image

Manager
Manager
User avatar
G
Joined: 06 Sep 2018
Posts: 171
Location: Pakistan
Concentration: Finance, Operations
GPA: 2.87
WE: Engineering (Other)
GMAT ToolKit User Premium Member Reviews Badge CAT Tests
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 13 Oct 2018, 00:37
let \(S\) be the sum of \(n\) peoples's ages.
\(\frac{S}{n}=15\)
\(S=15n\)

after adding one more person:
\(\frac{S+39}{n+1}=17\)
\(S+39=17n+17\)
\(15n+39=17n+17\)
\(2n=22\)
\(n=11\)
_________________

Hitting Kudos is the best way of appreciation. :)

Eric Thomas, "When you want to succeed as bad as you want to breathe, then you'll be successful."

GMATH Teacher
User avatar
G
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 542
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 29 Oct 2018, 08:17
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13

\(? = n\)

Perfect opportunity to use the homogeneity nature of the average:

\(\left. \begin{gathered}
\sum\nolimits_n { = 15 \cdot n} \hfill \\
39 + \sum\nolimits_n { = \sum\nolimits_{n + 1} { = \,\,\,} 17 \cdot \left( {n + 1} \right)\,\,\,} \, \hfill \\
\end{gathered} \right\}\,\,\,\,\,39 + 15n = 17n + 17\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,2n = 22\,\,\,\,\,\,\, \Rightarrow \,\,\,\,? = 11\)


This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.
_________________

Fabio Skilnik :: https://GMATH.net (Math for the GMAT) or GMATH.com.br (Portuguese version)
Course release PROMO : finish our test drive till 30/Dec with (at least) 50 correct answers out of 92 (12-questions Mock included) to gain a 50% discount!

Target Test Prep Representative
User avatar
P
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 4295
Location: United States (CA)
Re: The average age of a group of n people is 15 yrs. One more person aged  [#permalink]

Show Tags

New post 30 Oct 2018, 18:09
Bunuel wrote:
The average age of a group of n people is 15 yrs. One more person aged 39 joins the group and the new average is 17 yrs. What is the value of n?

(A) 9
(B) 10
(C) 11
(D) 12
(E) 13



We can create the equation:

(15n + 39)/(n + 1) = 17

15n + 39 = 17n + 17

22 = 2n

11 = n

Answer: C
_________________

Scott Woodbury-Stewart
Founder and CEO

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

GMAT Club Bot
Re: The average age of a group of n people is 15 yrs. One more person aged &nbs [#permalink] 30 Oct 2018, 18:09
Display posts from previous: Sort by

The average age of a group of n people is 15 yrs. One more person aged

  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®.