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If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha

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If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha [#permalink]

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New post 01 Sep 2016, 03:49
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Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha [#permalink]

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New post 01 Sep 2016, 07:04
Bunuel wrote:
If the average (arithmetic mean) of x and y is 40, and z – x = 60, what is the average of y and z?

A. 20
B. 50
C. 65
D. 70
E. 140


x+y/2 = 40
=> x+y = 80

x = z - 60...sub this value

z-60+y = 80
=>z+y = 140
=>z+y/2 = 70.

IMO option D.

OA please..will correct if I missed anything.

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Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha [#permalink]

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New post 06 Sep 2016, 14:13
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Bunuel wrote:
If the average (arithmetic mean) of x and y is 40, and z – x = 60, what is the average of y and z?

A. 20
B. 50
C. 65
D. 70
E. 140


Another approach is the assign values to x, y and z that satisfy the given conditions.

The average (arithmetic mean) of x and y is 40
Okay, two "nice" values are: x = 40 and y = 40

z – x = 60
Since we've let x = 40, then it must be the case that z = 100

What is the average of y and z?
If y = 40 and z = 100, then the average of y and z = (40+100)/2 = 70

Answer:
[Reveal] Spoiler:
D


NOTE: there was nothing special about the values I chose for x, y and z, other than the fact that they satisfied the given conditions. ANY other set of numbers will also yield the same answer.
For example, we could have used x = 20, y = 60 and z = 80, and this would have led to the same answer.
Try your own values to confirm this.

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Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha [#permalink]

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New post 12 Dec 2016, 11:26
Nice one.
Here mean(x,y)=40
Sum(x+y)=40*2=80
hence x+y=80
and z-x=60
Adding the two equations we get => z+y=140
Hence mean = 140/2 = 70

Hence D

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Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha   [#permalink] 12 Dec 2016, 11:26
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