Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 27 May 2015, 12:04

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Is 20 the average?

Author Message
TAGS:
Manager
Joined: 22 Jun 2010
Posts: 57
Followers: 1

Kudos [?]: 20 [0], given: 10

Is 20 the average? [#permalink]  15 Jul 2010, 12:45
00:00

Difficulty:

(N/A)

Question Stats:

33% (01:47) correct 67% (01:49) wrong based on 7 sessions
Hi,
came across this just now and i believe the OA is wrong, please tell me what you think:

Is 20 the average (arithmetic mean) of u, v, w, and 20?

(1) u + v + w = 60

(2) u - v + w = 20, u + v - w =16

[Reveal] Spoiler:
OA was A...

I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...
Math Expert
Joined: 02 Sep 2009
Posts: 27512
Followers: 4319

Kudos [?]: 42442 [0], given: 6028

Re: Is 20 the average? [#permalink]  15 Jul 2010, 13:12
Expert's post
AndreG wrote:
Hi,
came across this just now and i believe the OA is wrong, please tell me what you think:

Is 20 the average (arithmetic mean) of u, v, w, and 20?

(1) u + v + w = 60

(2) u - v + w = 20, u + v - w =16

[Reveal] Spoiler:
OA was A...

I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...

Have you tried to solve these 2 equations?

When you add $$u-v+w=20$$ and $$u+v-w=16$$ you'll get $$u=18$$ and if you substitute the value of $$u$$ in these two equations you'll get: for 1. $$18-v+w=20$$ --> $$w-v=2$$ and for 2. $$18+v-w=16$$ --> $$w-v=2$$, so two identical equations, thus you won't be able to solve for $$w$$, $$v$$ or for $$w+v$$.

Statement to be sufficient you need $$n$$ distinct linear equations for $$n$$ variables.
_________________
Senior Manager
Joined: 25 Feb 2010
Posts: 477
Followers: 4

Kudos [?]: 52 [0], given: 9

Re: Is 20 the average? [#permalink]  19 Jul 2010, 08:10
you can;t solve from B.
u'll get the same equation.
_________________

GGG (Gym / GMAT / Girl) -- Be Serious

Its your duty to post OA afterwards; some one must be waiting for that...

Intern
Joined: 16 Jul 2010
Posts: 18
Followers: 1

Kudos [?]: 12 [0], given: 9

Re: Is 20 the average? [#permalink]  20 Jul 2010, 11:53
AndreG wrote:

[Reveal] Spoiler:
OA was A...

I believe it should be D - since adding the two equations provided in ST2 cancels out v + w, so we can solve for u, leaving us with 2 equations with 2 unknowns...

Using the information in 1) it is possible to solve for v and w in 2). However, in order for D to be correct, we would need to be able to solve for v and w using only the information in 2). Since 1) is sufficient and 2) is insufficient alone, the answer is A.
_________________

If you find my posts useful, please award me some Kudos!

Ms. Big Fat Panda
Status: Three Down.
Joined: 09 Jun 2010
Posts: 1923
Concentration: General Management, Nonprofit
Followers: 382

Kudos [?]: 1559 [0], given: 210

Re: Is 20 the average? [#permalink]  20 Jul 2010, 12:14
Expert's post
I think as people have pointed out already, you need to make sure you actually know that the equation is solvable. Don't just think that since it simplifies to two equations with two variables you'll be able to solve it. It needs to be two distinct equations.
Senior Manager
Joined: 20 Jul 2010
Posts: 270
Followers: 2

Kudos [?]: 47 [0], given: 9

Re: Is 20 the average? [#permalink]  21 Jul 2010, 12:55
We have to answer Is $$\frac{U+V+W+20}{4}$$=20? Or U+V+W+20 is 80

Option 1 gives sum total of all.
Option 2 alone doesn't

_________________

If you like my post, consider giving me some KUDOS !!!!! Like you I need them

Re: Is 20 the average?   [#permalink] 21 Jul 2010, 12:55
Similar topics Replies Last post
Similar
Topics:
10 The average of a certain set of numbers is 20 and its 11 03 Oct 2014, 13:20
Q20 In 1981 children in the United States spent an average 11 29 Oct 2007, 02:04
15 numbers between 20 and 30 (inclusive?), is their average 2 06 May 2006, 03:49
Is the average of 15 integers between 20 and 30 greater than 4 05 May 2006, 23:44
If the average (arithmetic mean) of x, y, and 20 is 10 4 01 Dec 2005, 13:31
Display posts from previous: Sort by