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Number Properties question (arithmetic mean)

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Intern
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Joined: 06 Oct 2009
Posts: 33
Schools: Ryerson University
Followers: 1

Kudos [?]: 7 [0], given: 7

Number Properties question (arithmetic mean) [#permalink] New post 01 Feb 2010, 16:51
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

80% (01:26) correct 20% (00:51) wrong based on 5 sessions
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.
Manager
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Joined: 02 Aug 2009
Posts: 111
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Re: Number Properties question (arithmetic mean) [#permalink] New post 01 Feb 2010, 16:55
(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

so answer choice B.

Hope that helps
Manager
Manager
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Status: Getting ready for the internship summer
Joined: 07 Jun 2009
Posts: 51
Location: Rochester, NY
Schools: Simon
WE 1: JPM - Treasury
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Kudos [?]: 18 [0], given: 23

Re: Number Properties question (arithmetic mean) [#permalink] New post 01 Feb 2010, 17:03
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

Answer is B.
Director
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Re: Number Properties question (arithmetic mean) [#permalink] New post 01 Feb 2010, 20:45
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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Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2793
Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35
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Re: Number Properties question (arithmetic mean) [#permalink] New post 02 Feb 2010, 09:22
Intern
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Joined: 06 Oct 2009
Posts: 33
Schools: Ryerson University
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Re: Number Properties question (arithmetic mean) [#permalink] New post 02 Feb 2010, 14:50
thanks for the replies.
Re: Number Properties question (arithmetic mean)   [#permalink] 02 Feb 2010, 14:50
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