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# Does the average (arithmetic mean) of a,b, and c equal c? 1.

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Does the average (arithmetic mean) of a,b, and c equal c? 1. [#permalink]

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05 Jan 2006, 19:25
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Does the average (arithmetic mean) of a,b, and c equal c?

1. c-a = c+b
2. c=0

I'm sure this is a joke question for some of you but can someone dumb down their answer/explanation for me on this one? I don't know the best way to tackle it. And the kaplan explanation is just not sinking in. thanks...
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05 Jan 2006, 19:28
The question is asking whether (a+b+c)/3 = c --> a+b+c = 3c --> a+b=2c

(1) c-a = c+b -> a+b=0. If a+b =0, the average of a+b+c = c/3. So the average of a,b and c is not equal to c, unless c is 0. Since we do not know c, this statememtn is not sufficient.

(2) c = 0. Not sufficient as we do not know a and b.

Ans C

Last edited by ywilfred on 05 Jan 2006, 19:45, edited 1 time in total.
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05 Jan 2006, 19:32
how do you get 2c=a+b for Statement 1? I got -a=b or a+b=0. Is it correct to say that Statement 1 is insufficient because it tells us nothing about C?

I am struggling so much with DS, I just can't wrap my head around the concepts of how to approach them.
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05 Jan 2006, 19:41
buckkitty wrote:
how do you get 2c=a+b for Statement 1? I got -a=b or a+b=0. Is it correct to say that Statement 1 is insufficient because it tells us nothing about C?

I am struggling so much with DS, I just can't wrap my head around the concepts of how to approach them.

Sorry, made a mistake. I'll rework that and post again later.
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05 Jan 2006, 19:47
I've edited my working and the answer is C. Is that what you got?
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05 Jan 2006, 19:54
C is the OA. I understand your answer now. I was unsure why A was insuff. but now I get it.... thanks!
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Re: DS-average from Kaplan workbook 4th ed. [#permalink]

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05 Jan 2006, 23:58
buckkitty wrote:
Does the average (arithmetic mean) of a,b, and c equal c?

1. c-a = c+b
2. c=0

I'm sure this is a joke question for some of you but can someone dumb down their answer/explanation for me on this one? I don't know the best way to tackle it. And the kaplan explanation is just not sinking in. thanks...

We need to see if (a+b+c)/3 = c

From stmt 1 we get a+b=0, nothing is known about c so insuff.
From stmt 2 we get c = 0 but nothing is known about a,b so insuff.
Combing we have all information for a,b and c. So this is suff.

Hence C.
Re: DS-average from Kaplan workbook 4th ed.   [#permalink] 05 Jan 2006, 23:58
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