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# If the average (arithmetic mean) of x and y is 60 and the average (ari

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Intern
Joined: 06 Oct 2009
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Schools: Ryerson University
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If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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01 Feb 2010, 17:51
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Question Stats:

86% (01:46) correct 14% (01:02) wrong based on 83 sessions

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If the average (arithmetic mean) of x and y is 60 and the average (arithmetic mean) of y and z is 80, what is the value of $$z - x$$?

(a) 70
(b) 40
(c) 20
(d) 10
(e) It cannot be determined from the information given.
[Reveal] Spoiler: OA
Manager
Joined: 02 Aug 2009
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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01 Feb 2010, 17:55
(X + Y)/2=60 (Z + Y)/2=80

So Z + Y=160
X+Y = 120
Subtract the equations

and we get Z - X (the Y's cancel) = 40

Hope that helps
Manager
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Location: Rochester, NY
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WE 1: JPM - Treasury
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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01 Feb 2010, 18:03
Write out the equations:

x + y = 120
y + z = 160

Get y alone:

y = 160 - z
y = 120 - x

Set them equal to one another and (z - x) appears:

160 - z = 120 - x
40 = z - x

Director
Joined: 03 Sep 2006
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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01 Feb 2010, 21:45
roceeet wrote:
If the average (arithmetic mean) of x and y is 60 and the average (arithmetic mean) of y and z is 80, what is the value of $$z - x$$?

(a) 70
(b) 40
(c) 20
(d) 10
(e) It cannot be determined from the information given.

x+y= 120 & y+z = 160

z-x = 160-120 = 40

Therefore "B"
CEO
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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02 Feb 2010, 10:22
Yes B ,

quite an easy question.
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Intern
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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02 Feb 2010, 15:50
thanks for the replies.
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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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18 Sep 2015, 21:30
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari [#permalink]

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19 Sep 2015, 17:17
Hi All,

While most Test Takers would use an algebra approach to answer this question (which is fine), this prompt can also be solved by TESTing VALUES....

We're told that (X+Y)/2 = 60 and (Y+Z)/2 = 80. With a little algebra, we can rewrite these equations as...

X+Y = 120
Y+Z = 160

We're asked for the value of Z-X....

IF....
X = 60
Y = 60
Z = 100

So, Z-X = 100-60 = 40

No matter what values you TEST for X, Y and Z, the answer will always be the same (go ahead and try it and you'll see!).

[Reveal] Spoiler:
B

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Re: If the average (arithmetic mean) of x and y is 60 and the average (ari   [#permalink] 19 Sep 2015, 17:17
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