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Intern  Joined: 22 Jun 2010
Posts: 36
Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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1 00:00

Difficulty:   35% (medium)

Question Stats: 80% (01:52) correct 20% (01:46) wrong based on 68 sessions

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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

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...
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Joined: 02 Sep 2009
Posts: 59561
Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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1
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

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.
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Senior Manager  Joined: 25 Feb 2010
Posts: 273
Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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you can;t solve from B.
u'll get the same equation.
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Intern  Joined: 16 Jul 2010
Posts: 17
Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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AndreG wrote:

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.
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Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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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.
Manager  Joined: 20 Jul 2010
Posts: 179
Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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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

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Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?  [#permalink]

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_________________ Re: Is 20 the average (arithmetic mean) of u, v, w, and 20?   [#permalink] 11 Aug 2017, 03:45
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