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If x, y, and z are numbers, is z = 18 ? [#permalink]

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30 Sep 2015, 12:10

Bunuel wrote:

SOLUTION

If x, y, and z are numbers, is z = 18 ?

(1) The average (arithmetic mean) of x, y, and z is 6 --> x + y + z = 6*3 = 18. We cannot say whether z = 18. Not sufficient.

(2) x = -y --> x + y = 0. Clearly insufficient.

(1)+(2) x + y + z = 18 --> 0 + z = 18 --> z = 18. Sufficient.

Answer: C.

Dear Bunnel, Here,Is it possible to guess that number could be in a fraction format too?like \(\frac{1}{5}\)+\(\frac{-1}{5}\)=0 for x+y=0
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