A TO B DS APPROACH QUESTION

[lightscameraaccion]

tried the general math forum. hope to have better luck here..

An example from MGMAT CAT (not looking for the answer):

Reiko drove from point A to point B at a constant speed, and then returned to A along the same route at a different constant speed. Did Reiko travel from A to B at a speed greater than 40 miles per hour?

(1) Reiko's average speed for the entire round trip, excluding the time spent at point B, was 80 miles per hour.

(2) It took Reiko 20 more minutes to drive from A to B than to make the return trip.

To me, this is a "yes" or "no" question and Reiko's exact speed is irrelevant because a sufficient answer, to me at least, can be that she traveled less than, equal to, or greater than 40 mph (to answer the question stem "Did Reiko travel from A to B at a speed greater than 40 miles per hour?" yes, if she did and no, if she didnt). Therefore, since she is traveling x mph, both statements look sufficient to me regardless whether her speed was actually greater than 40mph. I've read the DS section on MGMAT, and I feel like I am using the logic put forth in the book but I continue to get these types of questions wrong. This is just one particular example, however, I find myself in this situation a lot in DS. Can someone give me a little more clarity on how to answer these types of questions.

thanks!

(answer is A btw.)

[RonPurewal]

tried the general math forum. hope to have better luck here..

yes, we saw that -- and please don't do it again. i.e., "double posting" is against the forum rules.
at best it fills the forum with unnecessary clutter; at worst it will lead to the development of two different discussions about the same problem.

you only posted that message about 36 hours ago. we'll thank you to be a bit more patient than that.

Therefore, since she is traveling x mph, both statements look sufficient to me regardless whether her speed was actually greater than 40mph.

what is this "x" that you cite here? (remember, this is the math section, where "x" does and means certain very specific things; it's a bad idea to toss "x" around as cavalierly as you would in a casual conversation.)

in context, it sounds as though you're saying, "the speed is a constant value that you can find."
if that is indeed what you're saying, then it's wrong; both statements admit a large variety of possible speeds.

all of the possible speeds from A to B in statement 1 are greater than 40 mph, so statement 1 is sufficient.
(if reiko drove exactly 40 mph from A to B, she would need to teleport back from B to A in zero seconds to achieve an average speed of 80 mph. if she drove from A to B at a slower rate, then, even if she could teleport herself back, that average would still be impossible.)

statement 2, on the other hand, admits some speeds greater than 40 mph and some speeds less than 40 mph, so statement 2 is insufficient.
(for instance, if the trip is 1 mile each way, and she took 1 year and 20 minutes to get from A to B and 1 year to get back, then that's plainly less than 40 mph on average. on the other hand, if the trip is 1000 miles each way, and she took 21 minutes on the way there and 1 minute on the way back, then that's clearly much greater than 40 mph on average. if the statement admits examples as extreme as these, there's no need to do all the calculations.)

in any case, again, i may be completely misunderstanding what you wrote here, given that i don't quite know what the "x" in your post means. please explain, thanks.