jwamala wrote:
I'm still not too clear on when it is appropriate to stop and be confident on the solution choice. I got to the part with the 2 equations combined, but then I selected "e", hoping there wasn't a constraint trick bc we clearly have too few equations and multiple unknowns. For some reason, I'm coming up on the 2 min mark after checking all of the previous out and it takes me another 2 mins (and a lot of energy) to find the exact #'s in Bunuel's solution. Is there a way to be confident without getting exact values for price and quantity in the combined statements case?
bump:
MathRevolution,
VeritasPrepKarishma, etc.
Let me try to answer.
You have not completely figured out the main crux of the problem. You need to be
absolutely sure of whether the items were \(\leq\) 36 or > 36 . This will determine (for example) in statement 1 you need to use I =nx or I=1.5x(n-36)+36x (lets calls them equations 1.a and 1.b respectively). So, you get 2 distinct equations with no basis to eliminate either one. Thus this statement is NOT sufficient.
You will be able to use I=nx if x \(\leq\) 36 but if it is > 36, then you must use I=1.5x(n-36)+36x. This ambiguity makes this statement NOT sufficient.
You can now see that there might be a catch in this question based on analysis of statement 1 alone. Now, go onto statement 2 and you will again realize that there is no basis to eliminate 1 of the 2 possible equations (lets calls them equations 2.a and 2.b respectively) as you still have not been provided any information about the number of the items. They can be \(\leq\) 36 but at the same time can also be >36. We have no justification to choose 1 option over the other.
Again, you get 2 more distinct equations , making statement 2 not sufficient alone.
For combining the 2 statements, you can now clearly see that you can have the following 2 sets of distinct equations:
1. 1.a and 2.a or
2. 1.b and 2.b
Either way, you will not be getting the same answer ---> E is thus the correct answer. But be careful about this step as if you do get the same result for 'x' or 'n' from the 2 systems of equations, then it will be C instead of E.
In totality, it took close to 1-1.5 minutes to analyse both statements individually with another 45-60 seconds to analyse both statements together and mark E as the answer.
Remember that in GMAT Quant, you need to spend an AVERAGE of 2 minutes per question and not more. This does not mean that all questions will take you full 2 minutes. Some of the questions are bound to take less than 2 minutes while some of them will take you >2 minutes, bringing the average close to 2 minutes per question.
As this is a 'difficult' question as categorized by the GMATCLUB timer results, it is fine if you spent 2-3 minutes on this question. In GMAT, you should be able to recover this time if you know how to pick your battles and move on.
Hope this helps.
P.S.:
1. Having 2 equations for 2 variables may or may not sufficient to give you a sufficient answer.
Example, 2a+3b=6 and 4a+6b=12 are although 2 equations but they are NOT distinct and you will not get a unique value for a,b. Thus you need to check for DISTINCT equations and not just any equations while solving for variables.
2. Lets say you ended up getting 2 systems of equations as
a) 2x+3y=4 and x+y=4 ,you get x=3 and y=1
b) 3x+4y=13 and 2x+y=7, you again get x=3 and y=1
Thus in this case, you must mark C as you are getting the same unique values for x and y.
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