santosh93 wrote:
gmat2805 wrote:
If |a + 5| = |b + 5| what is the value of a + b?
(1) b > 5 and a < 5
(2) b = 10
I think this question doesn't require Data statements to solve the problem.
Consider |a+5|=|b+5|
Squaring both the sides,
\((a+5)^2=(b+5)^2\)
Or, \(a^2+10a+25=b^2+10b+25\)
Or, \(a^2-b^2=-10 (a-b)\)
or, \(a+b=-10\) which is what the question asks for.
This problem requires
"a+b" value and
isn't concerned with values of a or b. Hence determining them using (1) b > 5 and a < 5 ;(2) b = 10 seems meaningless
PS:The concept of Data Sufficiency(DS) in GMAT is the find out whether statements(supporting data) are
sufficient to determine the answer. But here I statement became unnecessary or superfluous data in determining the answer. I believe GMAT doesn't ask the above question under the DS category.
Hi santosh93,
The initial information in a DS prompt is NEVER enough to conclusively answer the question - so if you think that you are facing a prompt in which you don't need any additional information, then it's likely that you are making some type of logic mistake while thinking about the prompt.
By working through the math steps that you've listed, you've fundamentally changed the original equation (and 'divided out' a potential solution). Consider the following two examples, based on the original equation:
|A + 5| = |B + 5|
IF.... A = 1 and B = 1, then |6| = |6| and the answer to the question is 1+1 = 2
IF.... A = 5 and B = -15, then |10| = |-10| and the answer to the question is 5 + (-15) = -10
Based on just the original equation, there is clearly more than one potential answer (so the assumption that the answer must be -10 is incorrect - and you need more information to determine whether there is just one answer or multiple answers).
GMAT assassins aren't born, they're made,
Rich
Thank you for the reply. Now I understand where I possibly went wrong while solving the original equation. I believe it was this step
instead of dividing out a potential solution, I should consider it as a possible answer.
Hence I would require support statements to concretely answer the problem.