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Help with advanced question

by leswm » Thu May 17, 2007 7:31 pm
I found the manhattan gmat question of the week:

If abc is not 0, what is the value of ? (a^3 + b^3 + c^3) / abc
( a^3 is a-cubed, b^3 is b-cubed...)

(1) |a|=1, |b|=2, |c|=3

(2) a + b + c = 0

(A) Statement (1) alone is sufficient, but statement (2) alone is not sufficient.
(B) Statement (2) alone is sufficient, but statement (1) alone is not sufficient.
(C) BOTH statements together are sufficient, but NEITHER statement alone is sufficient.
(D) Each statement ALONE is sufficient.
(E) Statements (1) and (2) TOGETHER are NOT sufficient.

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My answer was B, but it was after I plugged in and that took a while. Is there some property of numbers that can help me solve this one quick?
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Source: — Data Sufficiency |
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Re: Help with advanced question

by jayhawk2001 » Thu May 17, 2007 9:39 pm
leswm wrote:I found the manhattan gmat question of the week:

If abc is not 0, what is the value of ? (a^3 + b^3 + c^3) / abc
( a^3 is a-cubed, b^3 is b-cubed...)

(1) |a|=1, |b|=2, |c|=3

(2) a + b + c = 0
(a+b+c)^3 = a^3 + b^3 + c^3 +3ab(a+b+c) + 3bc(a+b+c) + 3ac(a+b+c) - 3abc

2 tells us that a+b+c = 0. So, a^3+b^3+c^3 = 3abc

So, (a^3+b^3+c^3) / abc = 3 always

Hence B
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by Cybermusings » Fri May 18, 2007 5:38 am
I found the manhattan gmat question of the week:

If abc is not 0, what is the value of ? (a^3 + b^3 + c^3) / abc
( a^3 is a-cubed, b^3 is b-cubed...)

(1) |a|=1, |b|=2, |c|=3

(2) a + b + c = 0


Statement I : Clearly insufficient since we do not know the actual values...we only know absolute values; hence the value of the equation can swing in many directions depending on actual values

Statement II : We can derive that all the 3 values do not have the same sign since none of them are 0; hence if a =3, b=2 and d=-5 value of the equation would be 3
Plug in any value and you will get the same answer

hence B
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