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Re: DS_ M03, question 19 [#permalink]
10 Jan 2008, 05:20

1. tells us that a = 0 or 2. INSUFFICIENT 2. since (a+b)^2 = (a^2+2ab+b^2) the whole fraction = 1. 1-1 = 0 and (b/c) = 0 so b must be 0. as long as one of the 3 integers is 0 abc will = 0 as well

Re: DS_ M03, question 19 [#permalink]
10 Jan 2008, 08:58

Thanks. I understood why statement 1 didn't work but couldn't figure out how statement 2 lead to B=0.

Now I get it. [b/c] = 0, where c cannot = 0 (given), so b must =0. I kept thinking [b/c] must =1 and forgot to take into account the last part that says [b/c] actually equals 0.

Re: DS_ M03, question 19 [#permalink]
10 Jan 2008, 09:59

misterJJ2u wrote:

a , b , and c are integers. Is abc = 0?

1) a^2 = 2a 2) (b/c) = [[(a+b)^2] / [a^2 + 2ab + b^2]] - 1; where a does not equal -b and c does not equal 0;

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient EACH statement ALONE is sufficient Statements (1) and (2) TOGETHER are NOT sufficient

Answer is B Statement 1: does not give any information about a.b.c---> Insufficient Statement 2: Can be rewrite as b/c = [(a+b)^2/(a+b)^2]-1 b/c = 1-1 = 0 which gives product of a,b and c is zero. Hence Sufficient

Re: a , b , and c are integers. Is abc = 0? 1) a^2 = 2a 2) (b/c) [#permalink]
05 Jul 2013, 11:16

Expert's post

jacg20 wrote:

I saw this question in a gmat club test, and I still have some doubts about the answer.

How can i reduce the expresion [(a+b)^2/(a+b)^2], if we don't know whether (a+b)^2 is 0 or not. ¿??

Thanks in advance for your help!

BELOW IS REVISED VERSION OF THIS QUESTION:

Is abc = 0 ?

In order abc = 0 to be true at least one of the unknowns must be zero.

(1) a^2 = 2a --> a^2-2a=0 --> a(a-2)=0 --> a=0 or a=2. If a=0 then the answer is YES but if a=2 then abc may not be equal to zero (for example consider: a=2, b=3 and c=4). Not sufficient.

(2) b= \frac{(a*\sqrt{c}+b*\sqrt{c})^2}{a^2+2ab+b^2} - c --> b= \frac{c*(a+b)^2}{(a+b)^2} - c --> b=c-c --> b=0. Sufficient.

Answer: B.

If a+b were equal 0, then \frac{c*(a+b)^2}{(a+b)^2} would be undefined and b= \frac{c*(a+b)^2}{(a+b)^2} - c (which is given as a true statement) wouldn't make sense.