BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Mean

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 152
Joined: Fri Apr 24, 2015 1:39 am
Location: Rourkela Odisha India
Thanked: 2 times
Followed by:3 members
GMAT Score:650

Mean

by akash singhal » Wed Nov 04, 2015 6:27 am
If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the
mean M of the set increase?
(1) Z = 60 (2) N = Z / M


OE C
Please Explain
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 113
Joined: Wed Dec 07, 2011 7:20 am
Thanked: 3 times

by manik11 » Wed Nov 04, 2015 7:11 am
Hi akash,

From the info given in the question we can deduce the following

M = (60+z)/6

Now if you multiply each number of the set by 'N' then

M = N(60+z)/6

Percentage change in M would be [M(new) - M(old)]/M(old) * 100%
This turns out to be

[N(60+z)/6 - (60+z)/6] / (60+z)/6
Factor out (60+z)/6 and you'll be left with N-1 (So you essentially need the value of N)

1) Z = 60
You can find the exact value of M from this. (No need to calculate though)
N is unknown, hence NOT Sufficient

2) N = Z/M
Z could have any value, hence NOT Sufficient

Combine both the statements and you have an exact value of M from Statement 1 and Statement 2 will give you a value of N

These two pieces of information are sufficient to calculate the percent change in N
Combined the statements are sufficient

OA : C

I would really appreciate if an expert could show a time efficient approach to this question.
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Wed Nov 04, 2015 8:05 am
akash singhal wrote:If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase?
(1) Z = 60 (2) N = Z / M
If every value in Set X is multiplied by a factor of N=2, then the value of mean M will also be multiplied by a factor of N=2.
If every value in Set X is multiplied by a factor of N=3, then the value of mean M will also be multiplied by a factor of N=3.
If every value in Set X is multiplied by a factor of N=10, then the value of mean M will also be multiplied by a factor of N=10.
Implication:
If we know the value of N, we can determine by what percent mean M will increase.

Question stem, rephrased:
What is the value of N?

Statement 1: Z=60
Since every value in Set X is known, the value of M can be determined.
No information about N.
INSUFFICIENT.

Statement 2: N = Z/M
Since the values of Z and M are unknown, no way to determine the value of N.
INSUFFICIENT.

Statements combined:
Statement 1: Z=60 enables us to determine the value of M.
Statement 2: Z=60 and the value of M will enable us to determine the value of N.
SUFFICIENT.

The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Post new topic Post Reply
• Page 1 of 1