DS : The sum of the integers in list S

[aagar2003]

answer = (e).

incidentally, if this problem is supposed to say that the integers are positive or non-negative (and the original poster simply forgot this caveat), then the problem is much easier, and the answer is different (at a glance i think it would be (a)).

thanks for the examples and answer. I agree OA is wrong.

[RonPurewal]

sure

[labralege.89]

ah, evil.

to get at the heart of this problem, you must realize that "greater" is NOT the same thing as "farther away from zero".
for positive numbers, these two concepts are the same, but they are not so for negative numbers (for which the the greater number is actually closer to zero).
that realization is the crux of this problem.

see, here's the deal:
the SUM is the same for each of the two sets. therefore, since average = (sum) / (# of data points), the average will be CLOSER TO ZERO if there are more data points.

the problem is that this doesn't mean that the average is lower. if the sum is negative, then just the opposite will occur.

examples:
if S = 2, 2, 2 and T = 3, 3, then the sums are both 6, the average of S is less (2 vs. 3), and S has more integers.
if S = -3, -3 and T = -2, -2, -2, then the sums are both -6, the average of S is less (-3 vs. -2), and S has fewer integers.
so (a) is insufficient.

if T = 2, 2, 2 and S = 3, 3, then the sums are both 6, the median of S is greater (3 vs. 2), and S has fewer integers.
if T = -3, -3 and S = -2, -2, -2, then the sums are both -6, the median of S is greater (-2 vs. -3), and S has more integers.
so (b) is insufficient.

together:
this takes a little more creativity.
if S = -7, 9, 10 and T = 6, 6, then the sums are both 12, the average of S is less (4 vs. 12), the median of S is greater (9 vs. 6), and S has more integers.
if S = -6, -6 and T = -10, -9, 7, then the nums are both -12, the average of S is less (-6 vs. -4), the median of S is greater (-6 vs. -9), and S has fewer integers.
so, insufficient.

answer = (e).

incidentally, if this problem is supposed to say that the integers are positive or non-negative (and the original poster simply forgot this caveat), then the problem is much easier, and the answer is different (at a glance i think it would be (a)).

Ron, how can it be possible to be so clever? :)

Thank you for your explanations. Are real GMAT exam questions as tough as those in the GMATprep?? I wish they were similar to questions in OG.

[RonPurewal]

Thank you for your explanations. Are real GMAT exam questions as tough as those in the GMATprep?? I wish they were similar to questions in OG.

the GMAT is adaptive -- so the answer to this question depends, of course, on how well you're doing on the exam.

[sachin.w]

Hi Ron,

examples:
if S = 2, 2, 2 and T = 3, 3, then the sums are both 6, the average of S is less (2 vs. 3), and S has more integers.
if S = -3, -3 and T = -2, -2, -2, then the sums are both -6, the average of S is less (-3 vs. -2), and S has fewer integers.
so (a) is insufficient.

if T = 2, 2, 2 and S = 3, 3, then the sums are both 6, the median of S is greater (3 vs. 2), and S has fewer integers.
if T = -3, -3 and S = -2, -2, -2, then the sums are both -6, the median of S is greater (-2 vs. -3), and S has more integers.
so (b) is insufficient.

together:
this takes a little more creativity.
if S = -7, 9, 10 and T = 6, 6, then the sums are both 12, the average of S is less (4 vs. 12), the median of S is greater (9 vs. 6), and S has more integers.
if S = -6, -6 and T = -10, -9, 7, then the nums are both -12, the average of S is less (-6 vs. -4), the median of S is greater (-6 vs. -9), and S has fewer integers.
so, insufficient.

How do you generate numbers that meet your requirement i.e to prove yes /no in a DS prob in less than 2 or 3 mins?

If there's a way to generate numbers quickly, we could save a lot of time.. and the problem can be solved in a very little time.

[jnelson0612]

Sachin, practice is really huge in this area. Ron is very good at this because he's done a ton of these problems and he knows what to do.

I would just look at either statement and try to come up with a very short list of small numbers for one set, using all the constrains. Then I would look at the constraints again and try to come up with another list that, with as few members as possible, abides by the constraints. Answer the question. Then look at how you can tweak one of the sets to get a different answer.

I would highly recommend that you take some time and play with putting these numbers together. Then once you feel as if you have a good handle on it, explain to someone else how you came up with your numbers. Explaining your own thought process will help you solidify in your mind how to do this.

[sachin.w]

Thanks a lot, Jamie. Apparently,this is one area I am trying to master.

This ,once done, will help me immensely.
I will follow your advice and will definitely play with the numbers and will definitely teach the same to somebody to cement the concept/skill gained through practice.

Best Regards,
Sachin

[RonPurewal]

you may also want to try making up your own problems (with similar topics).
you don't necessarily have to try to make problems that are as complex as the official ones, but "being on the other side" will definitely deepen your understanding.

[NL]

I think the trick of this type of question is that: from a rule (or an observation-Ron) that is true to a restricted number range, the question asks whether it is true for a bigger range. So the main task is to consider all possible cases, which are difficult to come up with for people who don’t play enough with numbers.

I’ll use this observation to guess the answer for this problem instead of twisting my neuron. Any better guessing strategy?

P/s: Don’t you say we shouldn’t question GMAC’s questions, Ron? Maybe this case is an exception :)

[RonPurewal]

I wouldn't pay much mind to this problem. When putting it into the software, they probably just forgot to include the "positive" stipulation.

To write a problem demanding such specific and nuanced exceptions would violate absolutely everything about how GMAC creates problems in general, so I think it's safe to assume the problem was simply mistranscribed.

[NinaP494]

The sum of integers in list S is the same as the sum of the integers in T. Does S contain more integers than T?
can we also interpret the above statement to mean that " s and t may also contain decimals along with integers but only sum of their integers is equal?" I am just trying to see how closely we should adhere to the language of the GMAC questions. Thanks

[RonPurewal]

The sum of integers in list S is the same as the sum of the integers in T. Does S contain more integers than T?
can we also interpret the above statement to mean that " s and t may also contain decimals along with integers but only sum of their integers is equal?" I am just trying to see how closely we should adhere to the language of the GMAC questions. Thanks

this would be irrelevant anyway, since the question deals only with the integers. nothing would change.

[RonPurewal]

MUCH MORE IMPORTANTLY—
there are NEVER, EVER, EVER any "trick questions" on this exam.
never.
really, never ever ever. if you think of a "gotcha" or "tricky" interpretation of something, IMMEDIATELY discard that interpretation, and solve the problem the way it was clearly meant to be solved.

if this test contained "trick questions", then it would be a completely useless instrument. in fact, such questions would directly select AGAINST the type of candidate this test is designed to favor!

[NinaP494]

Thats an important insight. Thanks

MUCH MORE IMPORTANTLY—
there are NEVER, EVER, EVER any "trick questions" on this exam.
never.
really, never ever ever. if you think of a "gotcha" or "tricky" interpretation of something, IMMEDIATELY discard that interpretation, and solve the problem the way it was clearly meant to be solved.

if this test contained "trick questions", then it would be a completely useless instrument. in fact, such questions would directly select AGAINST the type of candidate this test is designed to favor!

[RonPurewal]

you're welcome.