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#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha

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Math Expert V
Joined: 02 Sep 2009
Posts: 59587
If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

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Difficulty:   5% (low)

Question Stats: 87% (01:08) correct 13% (01:12) wrong based on 128 sessions

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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

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Retired Moderator G
Joined: 26 Nov 2012
Posts: 554
Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

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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

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.
GMAT Club Legend  V
Joined: 12 Sep 2015
Posts: 4125
Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

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Top Contributor
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

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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Current Student D
Joined: 12 Aug 2015
Posts: 2548
Schools: Boston U '20 (M)
GRE 1: Q169 V154 Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

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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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Manager  B
Joined: 03 Aug 2017
Posts: 92
Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

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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

Create 2 equations to solve this one

1) Mean of X& Y= 40

= (x+y)/2 = 40
X+Y =80
or Y =80- X

2) Second equation'

z= 60 +X

Target question is to find the avg of Y and Z

so (80-X + 60+X) /2 = 140/2 =70 ans choice D
Target Test Prep Representative V
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Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha  [#permalink]

### Show Tags

1
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

Since the average of x and y is 40, we have:

(x + y)/2 = 40

x + y = 80

We are also given that z - x = 60.

Adding together the two equations, we have:

y + z = 140

So the average of y and z is:

(y + z)/2 = 140/2 = 70

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If you find one of my posts helpful, please take a moment to click on the "Kudos" button. Re: If the average (arithmetic mean) of x and y is 40, and z – x = 60, wha   [#permalink] 11 Oct 2019, 15:50
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