Again GMAT prep problem

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Again GMAT prep problem

by olika » Mon Jun 23, 2008 8:31 am
If a, b, and c are integers, what is the value of a?
1) (a-7)(b-7)(c-7)=0
2) bc=18

The answer "Both statements together are sufficient"

I just can't understand how it can be sufficient, if we have three unknowns and only two equations. :(
It seems there is no enough time during real GMAT test to multiply all terms to figure out the answer.

Sorry, if this question has appeared not the first time. I didn't find the answer.

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by atlantic » Mon Jun 23, 2008 8:39 am
Hi Olika,

That is new for me. Is it from GMAT Prep?

(1) says that a=7 or b=7 or c=7, so INSUFF, as when b=7 'a' can be any other integer.

(2) bc=18, tell us nothing about A so INSUFF

(1+2) if bc=18 then neither 'b' nor 'c' can be 7 (remind that a, b and c must be integers), since 18 is not a multiple of 7. If 'b' and 'c' are not 7 then 'a' must be.

Answer C

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by olika » Mon Jun 23, 2008 8:46 am
Hi!
Thank you very much for clear explanation!
Right now the decision seems obvious for me :)
How can I not to guess by myself!?

Yes, that question was from GMAT Preparation