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Expert's post 00:00

Question Stats: 30% (00:20) correct 69% (00:52) wrong based on 23 sessions
$$\frac{1-x}{x-1}=\frac{1}{x}$$

 Quantity A Quantity B $$x$$ $$\frac{-1}{2}$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Practice Questions
Question: 8
Page: 339
Difficulty: medium
[Reveal] Spoiler: OA

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Expert's post
Solution

Since the denominator must be different from zero we do have that x is different from 1 and zero

Multiplying both sides we do have: $$x-x^2=x-1$$ from which$$x^2=1$$

Our roots are $$x=1$$ or $$x=-1$$ but we already know that x must be different from 1. So the only value we do have is $$x=-1$$

$$-1 < \frac{1}{2}$$

The answer is $$B$$
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"we already know that x must be different from " from where you already known that? GRE Prep Club Legend  Joined: 07 Jun 2014
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GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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Expert's post
Hey,

The relation $$\frac{1-x}{x-1}=\frac{1}{x}$$ is already told to be true.

Now if you put x=1 the LHS becomes undefined and and if x=0 then RHS becomes undefined.

Hence X cannot be 0 or 1.
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Sandy
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Expert's post
Carcass wrote:
$$\frac{1-x}{x-1}=\frac{1}{x}$$

 Quantity A Quantity B x $$\frac{-1}{2}$$

Aside: from the given equation, we know that x ≠ 0 and we know that x-1 ≠ 0
Here's why:
If x = 0, we get: (1-0)/(0-1) = 1/0
Simplify to get: -1 = 1/0 DOESN'T WORK
So, x ≠ 0

Likewise, if x-1 = 0, then x = 1
If we plug in 1 for x, we get: (1-1)/(1-1) = 1/1
Simplify to get: 0/0 = 1/1 DOESN'T WORK
So, x-1 ≠ 0

--------------------------------
Okay, now for a different approach....

Notice that 1-x = -1(-1 + x) = -1(x-1)
So, let's take (1-x)/(x-1) = 1/x and replace (1-x) with -1(x-1)

We get: -1(x-1)/(x-1) = 1/x
Simplify to get: -1 = 1/x
Solve to get: x = -1

So, we have:
Quantity A: -1
Quantity B: -1/2

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(1-x)/(x-1)=1/x
-1(x-1)/(x-1)=1/x
therefore, x=-1 then qty b=-0.5 so qty b is greater Re: 1-x/x-1=1/x   [#permalink] 15 Nov 2017, 23:39
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