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If the average (arithmetic mean) of 3 integers x, y, z is 10, what is

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If the average (arithmetic mean) of 3 integers x, y, z is 10, what is  [#permalink]

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New post 14 Aug 2018, 17:45
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A
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[Math Revolution GMAT math practice question]

If the average (arithmetic mean) of 3 integers x, y, z is 10, what is the value of z?

1) x=1
2) x=5-y

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Re: If the average (arithmetic mean) of 3 integers x, y, z is 10, what is  [#permalink]

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New post 14 Aug 2018, 19:57
MathRevolution wrote:
[Math Revolution GMAT math practice question]

If the average (arithmetic mean) of 3 integers x, y, z is 10, what is the value of z?

1) x=1
2) x=5-y


So x+y+z=30......z=?
1) x=1..
y+z=29...
Insufficient
2) x=5-y
x+y=5..
So z=30-5=25
Sufficient

B
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Re: If the average (arithmetic mean) of 3 integers x, y, z is 10, what is  [#permalink]

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New post 15 Aug 2018, 07:45
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

The original condition gives \(\frac{( x + y + z )}{3} = 10\) or \(x + y + z = 30\). Rearranging yields \(z = 30 – ( x + y ).\) Condition 2) gives \(x + y = 5\), so condition 2) is sufficient .


Condition 1) is not sufficient since it gives no information about the value of y.

Therefore, B is the answer.

Answer: B
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Re: If the average (arithmetic mean) of 3 integers x, y, z is 10, what is  [#permalink]

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New post 15 Aug 2018, 09:26
Given: \(\frac{x+y+z}{3}\)= 10; x+y+z=30

1) x=1. No inf of y. So z cannot be calculated.[Insuff]

2) x= 5-y; x+y=5; Put this value in original equation above. Value of z can be found [Suff]

Answer: B.
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Re: If the average (arithmetic mean) of 3 integers x, y, z is 10, what is   [#permalink] 15 Aug 2018, 09:26
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