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Number Properties question (arithmetic mean)

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Number Properties question (arithmetic mean) [#permalink] New post 01 Feb 2010, 17:51
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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.
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Re: Number Properties question (arithmetic mean) [#permalink] New post 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

so answer choice B.

Hope that helps
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Re: Number Properties question (arithmetic mean) [#permalink] New post 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

Answer is B.
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Re: Number Properties question (arithmetic mean) [#permalink] New post 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"
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Re: Number Properties question (arithmetic mean) [#permalink] New post 02 Feb 2010, 10:22
Yes B ,

quite an easy question.
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Re: Number Properties question (arithmetic mean) [#permalink] New post 02 Feb 2010, 15:50
thanks for the replies.
Re: Number Properties question (arithmetic mean)   [#permalink] 02 Feb 2010, 15:50
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