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If the average of x and y equals 40, the average of y and z

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If the average of x and y equals 40, the average of y and z [#permalink] New post 22 Jul 2019, 09:10
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Question Stats:

84% (01:19) correct 15% (01:57) wrong based on 19 sessions
If the average of x and y equals 40, the average of y and z equals 60, and the average of x, y, and z equals 30, then the average of x and z equals what?

[Reveal] Spoiler: OA
-10

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Re: If the average of x and y equals 40, the average of y and z [#permalink] New post 23 Jul 2019, 06:52
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Carcass wrote:
If the average of x and y equals 40, the average of y and z equals 60, and the average of x, y, and z equals 30, then the average of x and z equals what?

[Reveal] Spoiler: OA
-10


The average of x and y equals 40
We can write: (x+y)/2 = 40
Multiply both sides by 2 to get: x + y = 80

The average of y and z equals 60
We can write: (y+z)/2 = 60
Multiply both sides by 2 to get: y + z = 120

The average of x, y, and z equals 30
We can write: (x+y+z)/3 = 30
Multiply both sides by 3 to get: x + y + z = 90

IMPORTANT: We need to find the sum of x and z

Take:
x + y + z = 90
y + z = 120
Subtract the bottom equation from the top equation to get: x = -30

Take:
x + y + z = 90
x + y = 80
Subtract the bottom equation from the top equation to get: z = 10

Average of x and z = (x + z)/2 = [(-30) + 10]/2 = (-20)/2 = -10

Answer: -10

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Re: If the average of x and y equals 40, the average of y and z   [#permalink] 23 Jul 2019, 06:52
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If the average of x and y equals 40, the average of y and z

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