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city B is 5 miles east of city A. city C is 10 miles [#permalink]
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28 Feb 2005, 01:20
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city B is 5 miles east of city A. city C is 10 miles southeast of city B. which of the following is the closest to distance from city A to city C?
a 11miles
b 12
c 13
d 14
e 15



Intern
Joined: 09 Jan 2005
Posts: 21

x^2=25^2+10^2
SOlve for x and you'll get 11 as the closest answer.
A



Senior Manager
Joined: 19 Feb 2005
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Location: Milan Italy

11 for me too.
I get sqrt[125] as the distance b/w A and C



SVP
Joined: 03 Jan 2005
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The way I did it is this: Draw a line that is perpendicular toward line AB. Call the intersection D.
Since angle CBD is 45 degree, we can get BD=DC=5sqrt(2).
Therefore AC^2=AD^2+CD^2=(5+5sqrt(2))^2+(5sqrt(2))^2
AC=5sqrt(5+2sqrt(2))=14



SVP
Joined: 03 Jan 2005
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Another way, perhaps easier in calculation, is this.
5sqrt(2) is app 7. Therefore the triangle has a side 7, and 12 (=5+7). And we know the long side would be 13. However we know the two short sides are really a little longer than 7 and 12, so the long side must be a little longer than 13. Therefore 14.
I'd be sure about this answer if there isn't a choice of 15. However since there ARE two answers above 13, I'd use this as a sanity check for my other answer, or I'd useing this technique to make a quick guess if I'm short of time.



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Joined: 28 Dec 2004
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I'm confused
I think the rule being tested here is that the side of a triangle cannot be greater than the (sum of the other two sides) and cannot be less than the difference of the other two sides.
given that
what is the smallest possible value thats in between 15 and 5, is 11?
cant 11 be the answer....again we dont know what angle southeast it is...
if we have a 454590 triangle then there is no way that one side can be 10! it has sqrt(2)*5 which is less than 10.



VP
Joined: 18 Nov 2004
Posts: 1433

"D".....took some time to realize that souteast means 45 deg angle from the origin.
Draw a perpendicular from C towards north, call it D....now we know that
AC^2 = AD^2 + DC^2
AD = 5 + 10Cos 45
DC = 10Sin 45
solve for AC ~ 14



Senior Manager
Joined: 19 Feb 2005
Posts: 486
Location: Milan Italy

wow I did a huge mistake
because [5+5sqrt(2)]^2 is different from 5^2+5sqrt(2)^2
Last edited by thearch on 28 Feb 2005, 13:41, edited 1 time in total.



Senior Manager
Joined: 19 Feb 2005
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Location: Milan Italy

Is this right? OBVIOUSLY BC IS 10 NOT AC
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Manager
Joined: 24 Jan 2005
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Location: Boston

Yup 14 it is though all the choices are so close you really need to calculate.



Manager
Joined: 27 Jan 2005
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Location: San Jose,USA India

This is also same as finding the larger diagnal of a parellelogram where the sides are a and b.
I think it is something like this(I am not sure of the exact formula.Please correct me if you know ithe formula).
larger diagnal = sqrt(a^2+b^2+2abCosB). In our case, a=5,b=10 and B=90+45 degrees.



Manager
Joined: 11 Jan 2005
Posts: 101

"city B is 5 miles east of city A. city C is 10 miles southeast of city B. which of the following is the closest to distance from city A to city C? "
who stated that Southeast means : 45*.
I don t agree.
I would say 12.
12^2 is the closest of 125
and following that
C is still southeast of B
B is still east of A
Besides I doubt that such question will pop up during the quest



Manager
Joined: 11 Jan 2005
Posts: 101

Strange and inaccurate.
what is the OE then ? does it assume "Southeast" stands for 45 degree ?
if yes then D, if no, then I dont get it.
From which Editor, is the question?



VP
Joined: 30 Sep 2004
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Location: Germany

mdf2 wrote: Strange and inaccurate. what is the OE then ? does it assume "Southeast" stands for 45 degree ? if yes then D, if no, then I dont get it.
From which Editor, is the question?
i only have the OA ! no OE ! i dont know the editor !



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Joined: 03 Jan 2005
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Southeast: The direction or point on the mariner's compass halfway between due south and due east, or 135Â° east of due north.



Director
Joined: 27 Dec 2004
Posts: 897

fresinha12 wrote: I'm confused
I think the rule being tested here is that the side of a triangle cannot be greater than the (sum of the other two sides) and cannot be less than the difference of the other two sides.
given that what is the smallest possible value thats in between 15 and 5, is 11?
cant 11 be the answer....again we dont know what angle southeast it is...
if we have a 454590 triangle then there is no way that one side can be 10! it has sqrt(2)*5 which is less than 10.
You know that was the first thing that came to my mind and i do believe that is what's being tested. Based on the options, i would have picked D anyways since it is less than 15.
Now can someone please backup the theory that southeast is 45degrees? Please don't mislead us to memorize unfounded rules. thanks



Director
Joined: 27 Dec 2004
Posts: 897

mdf2 wrote: "city B is 5 miles east of city A. city C is 10 miles southeast of city B. which of the following is the closest to distance from city A to city C? "
who stated that Southeast means : 45*. I don t agree. I would say 12.
12^2 is the closest of 125 and following that C is still southeast of B B is still east of A
Besides I doubt that such question will pop up during the quest
I will love to believe this kinda of complexity won't pop up on the test. I know trignomerty is not tested and it seems a couple of people used trig to solve it thus i won't even waste my time internalizing this



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Joined: 03 Jan 2005
Posts: 2233

Folaa3 wrote: Now can someone please backup the theory that southeast is 45degrees? Please look at my post just before yours. It is the definition from the dictionary. Folaa3 wrote: I will love to believe this kinda of complexity won't pop up on the test. I know trignomerty is not tested and it seems a couple of people used trig to solve it thus i won't even waste my time internalizing this.
It may be a little stretched from the GMAT level. Or perhaps we could say this would be a hard level GMAT question. However you do not need to know trignomerty to solve this question. In other words, this is not totally out of scope of GMAT.
I think this is a good question. First, it tests your attention level. (Yes, can you correctly draw the triangle out? Did you notice it was southeast instead of south?) Second, it tests your understanding about straight triangles. (c^2=a^2+b^2) Third, it tests your arithmatic abilities. (The level of calculation is a little bit harder than a GMAT question normally requires, I believe. But if you can do it correctly, it means you would not have arithmatic problems for the eaiser level questions.)



Director
Joined: 27 Dec 2004
Posts: 897

Thanks Honghu



Director
Joined: 05 Jan 2005
Posts: 557

Now can someone please backup the theory that southeast is 45degrees? Please don't mislead us to memorize unfounded rules. thanks[/quote]
Southeast is actually 45degees. It's a fact in trignometry/bearing. If it were something else, say 60 degrees, it will have been stated that Point C is 60 degrees due south of B. This question actually seems to need trignomery, since we are given one angle as 135 degrees and two sides (0.5 A * B sin C). I also guessed between 14 and 15, and my guess was 14.










