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Airline pilots

by ironsferri » Fri Jun 04, 2010 11:32 am
A, B, C, D, and E are airline pilots with very busy travel schedules. Given that D is able to meet at any time that B cannot meet, do the schedules of A, B, C, D, and E allow three of these five individuals to meet together for two uninterrupted hours?

(1) Pilots A and C, who cannot meet together, are not able to end any meeting during the AM hours of any weekday.

(2) Pilots B and E, who can never meet for longer than 2 uninterrupted hours, are only available to meet for two straight hours starting at 10:30 PM on any weekday and not ending during the AM hours of any weekend day.


A and B and D are out because don't provide any info about other pilots.
Between C and E I picked E, because the questions sounded to general to provide a definitive YES or NO answer.

ALSO - what kind of difficulty level is this question???
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by uwhusky » Fri Jun 04, 2010 1:29 pm
This should be in Data Sufficiency, and I believe this would be a 700+ question...and I hate this question! =)
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by ironsferri » Fri Jun 04, 2010 1:31 pm
you're so right - sorry I posted it in the PS section.....:)
BTW, yes, it's a hella of a brain-teaser....
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by Testluv » Fri Jun 04, 2010 2:41 pm
Definintely a head-scratcher! I would rate this question about 750 although note you don't actually need ANY math theory or content to answer it. This question is testing your nerve. If you patiently reason your way through it, it can certainly be done inside of 2 to 2.5 minutes. Of course, trusting that you can get through it quickly enough while "patiently reasoning your way through it" takes nerve or guts.

_____________

Can three of these five pilots ever meet together?

From the stem we know that D is able to meet ANY time B cannot. This means that D is able to meet when B cannot, and also allows for (but does not establish) the possbility that B or D are both able to meet.

Other than that, we don't know that the other pilots are or are not able to meet, and we also don't know whether certain pilots, if able to meet, are or are not able to meet certain other pilots. There's a lot we don't know.

Therefore, in order to be sufficient, the statements will have to provide us with a lot of information. (It would be a good strategic move to guess E or maybe C on this question, and then move on).

(1) Definitely not enough info. For one thing we don't know about E, and we have no info about WHEN any of the other pilots can meet. Additionally, we still don't know about the stuff we didn't know about before we looked at (1).

(2) tells us that B and E can meet together starting at 10:30pm on any weekday. So that's two; but we don't know whether or not a third can join them. Insufficient.

(1) + (2)
We know from (1) that A and C can't meet together. So, out of that pair, only 1 is available to meet at any given time. But from (2), we know that B and E are "ONLY" available to meet starting at 10:30pm and not ending during the AM hours of any weekend day. Thus, B and E can ONLY meet Monday through Thursday beginning at 10:30 pm. If they meet at 10:30pm, the meeting will run 'til 12:30 am the next day. But from (1), we know that neither of A nor C can end any meeting during the AM hours of ANY weekday.

Thus, neither of A nor C can ever meet with either of B or E. And A can't meet with C. So, if you diagram it something like this

...........AxxxC
...........B.....D

you can see that you can't have the "horizontal block" AC, you can't have either of the "vertical blocks" AB or CD, and you can't have either of the "diagonal blocks" AD or BC. So, out of this quartet, that leaves B and D as the only pair whose meeting together hasn't been ruled out as a possibility; this doesn't meet that we know that B or D are for sure able to meet together.

We know from (2) that B and E are able to meet starting at 10:30pm on any weekday, so B and E are the only two pilots we know of that are for sure able to meet together at a certain time; we know for sure that A and C can't join them (B can't meet with either of A or C as discussed in the paragraph above) but whether D can join them (B and E that is), we cannot say. So, we don't know whether or not three of them can meet for two hours uninterrupted.

Choose (E).
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by gmatmachoman » Sun Jun 06, 2010 5:13 am
dada,

Just got sometime to ping u back.

I did go thru ur explanation. But at the outset, do we have "strict"regukation for weekend/weekday? Does GMAC defines it anywhere...

I assumed sat& sunday both to be weekend...
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by uwhusky » Sun Jun 06, 2010 6:33 am
Saturday and Sunday are part of the weekend, and it is a solid fact.
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by Testluv » Sun Jun 06, 2010 7:53 am
gmatmachoman wrote:dada,

Just got sometime to ping u back.

I did go thru ur explanation. But at the outset, do we have "strict"regukation for weekend/weekday? Does GMAC defines it anywhere...

I assumed sat& sunday both to be weekend...
Hey Govi. Yes, indeed, Sat and Sun are both weekend days.

But (2) says that those pilots are ONLY available to meet on weekday evenings. So far, this means that they are available to meet ONLY Mon-Fri 10:30pm. But then, we also learn in the rest of (2) that their meetings can't end in the AM hours of the weekend. Thus, B and E are ONLY available to meet Mon-Thurs, 10:30pm.
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