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dada sufficiency help

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dada sufficiency help

by linfongyu » Thu Jan 31, 2008 9:22 pm
hi,

please help.

What is the value of a+b+C?

1) The average (arithmetic mean) of a, b, and c is 4

2) abc = a^3 = 64 and a, b, and c are all integers.

i want to say that it's A, statement 1 is enough, 2 is not.
(a+b+c)/3 = 4
(a+b+c) = 12

abc = a^3 = 64, b and c could both be -4, or 4, so, can't solve...

but i get a lingering feeling that i'm missing something. please help.
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Re: dada sufficiency help

by Stuart@KaplanGMAT » Thu Jan 31, 2008 9:35 pm
linfongyu wrote:hi,

please help.

What is the value of a+b+C?

1) The average (arithmetic mean) of a, b, and c is 4

2) abc = a^3 = 64 and a, b, and c are all integers.

i want to say that it's A, statement 1 is enough, 2 is not.
(a+b+c)/3 = 4
(a+b+c) = 12

abc = a^3 = 64, b and c could both be -4, or 4, so, can't solve...

but i get a lingering feeling that i'm missing something. please help.
(2) abc = a^3 = 64

We know that a = 4, which means that bc = 16.

So, we could pick b = 1 and c = 16 or b = 2 and c = 8 (or lots of other combinations). For each set of numbers, we'll get a different value for a+b+c. Therefore, (2) is insufficient.

Choose (A).
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