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If w > x > y > z > 0, is z < 4?

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If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 14:14
2
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A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

36% (00:18) correct 64% (01:59) wrong based on 14 sessions

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If w > x > y > z > 0, is z \frac{1}{4}[/m].


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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 14:25
(1) We could transform the initial condition:
0<1/W<1/X<1/Y<1/Z
If Z>4, then 1/Z<1/4 and three other number 1/W, 1/Y, 1/X are also less than 1/4, so their sum could not be equal to 1. So (1) is sufficient to say that Z<4.

So, the answer is A

(2) alone does not say us anything about Z
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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 18:12
Given 0 < Z < y<X <w

1. sufficient
if z >4 => 1/z <0.25 , then the given sum will never be 1. Hence this is enough to say z cannot be greater than 4.

2. sufficient

w<4 =>z<w<4 => z<4, enough to answer the question.

Answer is D.
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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 19:05
@Spidy001, I've a query here :

if z >4 => 1/z <0.25 , then the given sum will never be 1. Hence this is enough to say z cannot be greater than 4.

How is the above true ? If z > 4 => z < 0.25 then z can have max value(s) as 0.24, 0.249 etc or lesser values as 0.05 etc. and the values of y, x and w can be more than this and hence the total may be 1, right ?

(2) is clearly sufficient as we have > W, and w > z so clearly z < 4.

Not sure if I'm doing anything wrong in the analysis of (1), someone please enlighten me.

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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 19:23
1
No.

As W>X>Y>Z

1/W < 1/X < 1/Y < 1/Z

Also as 1/Z < 1/4 ,

=> 1/W < 1/X < 1/Y < 1/Z < 1/4

so with this condition their sum will never be equal to 1.

Hope its clear now.







subhashghosh wrote:
@Spidy001, I've a query here :

if z >4 => 1/z <0.25 , then the given sum will never be 1. Hence this is enough to say z cannot be greater than 4.

How is the above true ? If z > 4 => z < 0.25 then z can have max value(s) as 0.24, 0.249 etc or lesser values as 0.05 etc. and the values of y, x and w can be more than this and hence the total may be 1, right ?

(2) is clearly sufficient as we have > W, and w > z so clearly z < 4.

Not sure if I'm doing anything wrong in the analysis of (1), someone please enlighten me.

Regards,
Subhash
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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 20:10
OA is D.

for 1) as Spidy said, if z >= 4 then, 1/z =< 0.25 and since w,x, and y are greater than z, 1/w, 1/x, 1/y and 1/z will all be less than 0.25 and their sum will never amount to 1. 4*(# less than .25)<1
Thus z has to be less than 4.
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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 22:21
Yes, I had mistaken this bit :

As W>X>Y>Z

1/W < 1/X < 1/Y < 1/Z

Thanks for your reply.

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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 20 Mar 2011, 22:58
if W>X>Y>Z>0, for positive integers 1/W<1/X<1/Y<1/Z

1. 1/W + 1/X + 1/Y + 1/Z = 1
To check whether Z > 4 or not, lets put Z = 5
this means 1/W + 1/X + 1/Y = 1-1/5= 4/5 or 0.8. average value of each term would be 0.266. But 1/z = 0.2. We know from question stem that 1/Z > 1/X , 1/Y, 1/Z. Thus we know z is not greater than 4. Hence 1 is sufficient to answer this question

2. 1/W >1/4 this implies that 1/Z >1/4. or Z<4. This also correctly answers the question.

Since both statements are sufficient by themselves, D
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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 12 Dec 2017, 22:42
Given W>X>Y>Z>0

Asked Z>4?

Stat#1:
1/W +1/X +1/Y +1/Z = 1 and W>X>Y>Z>0 can only possible if w,x,y,z are fractions so suff.

Stat#2:
1/W > 1/4 => w>4 { as w>0 } so suff.

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Re: If w > x > y > z > 0, is z < 4? [#permalink]

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New post 12 Dec 2017, 22:56
If w > x > y > z > 0, is z \frac{1}{y}>\frac{1}{x}>\frac{1}{w}[/m] and the question becomes whether \(\frac{1}{z}>\frac{1}{4}\)?

(1) \(\frac{1}{w} +\frac{1}{x} +\frac{1}{y} +\frac{1}{z} = 1\). Now, if \(\frac{1}{z}\leq{\frac{1}{4}}\) then all other three fractions will also be less than \(\frac{1}{4}\) and their sum (the sum of [b]four
numbers each of which is less than 1/4) can not add up to 1, hence \(\frac{1}{z}>\frac{1}{4}\). Sufficient.

(2) \(\frac{1}{w} > \frac{1}{4}\). Since \(\frac{1}{z}>\frac{1}{w}\) then \(\frac{1}{z}\) is also more than \(\frac{1}{4}\). Sufficient.

Answer: D.



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Re: If w > x > y > z > 0, is z < 4?   [#permalink] 12 Dec 2017, 22:56
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