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In the figure above, what is the value of b? (1) a+c+d=225 [#permalink]
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24 Apr 2006, 12:43
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In the figure above, what is the value of b?
(1) a+c+d=225
(2) da =55 == Message from GMAT Club Team == This is not a quality discussion. It has been retired. If you would like to discuss this question please repost it in the respective forum. Thank you! To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative  Verbal Please note  we may remove posts that do not follow our posting guidelines. Thank you.
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Manager
Joined: 13 Dec 2005
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Location: Milwaukee,WI

should be B
from figure a +b+c =180
==> a +b =180 c
a +b =d
so b= da
from (2) b =da = 55 so B is sufficient
From (1) you get a = 225 180 = 45 , we dont know anything about d so insufficient



Manager
Joined: 20 Nov 2004
Posts: 108

From (1), we get:
a + c + d = 225
c + d = 180
So a = 45. Not sufficient.
From (2), we get:
d  a = 55
d = 55 + a
180  c = 55 + a
a + 55 + c = 180
So b = 55 and therefore B.
Good question. I almost fell into the trap.



Director
Joined: 02 Mar 2006
Posts: 571
Location: France

Great! you're both right!
First, given the figure, how could we know that a c d is on a lign? I thought if that information is not given, we cannot suppose it. Tha's why I answered (E). The information give is just that a c b is a triangle...
Second point, I've learn in different GMAT DS tips, that for variables to be solved, there needs to be at least as much as equations as unknown. It doesn't seem to work if we consider following
So with (1) we have:
a+b+c=180
c+d =180
a + c + d = 225
4 variables and 3 equations are not enough to solve it => right
with (2)
a+b+c=180
c+d =180
ad=55
It 's the same, we have 4 variables and 3 equations => false
why can't we say it isn't enough to solve it. Where's the flaw?



GMAT Club Legend
Joined: 07 Jul 2004
Posts: 4971
Location: Singapore

karlfurt wrote: Great! you're both right!
First, given the figure, how could we know that a c d is on a lign? I thought if that information is not given, we cannot suppose it. Tha's why I answered (E). The information give is just that a c b is a triangle...
Second point, I've learn in different GMAT DS tips, that for variables to be solved, there needs to be at least as much as equations as unknown. It doesn't seem to work if we consider following
So with (1) we have: a+b+c=180 c+d =180 a + c + d = 225
4 variables and 3 equations are not enough to solve it => right
with (2) a+b+c=180 c+d =180 ad=55
It 's the same, we have 4 variables and 3 equations => false
why can't we say it isn't enough to solve it. Where's the flaw?
First, given the figure, how could we know that a c d is on a lign? I thought if that information is not given, we cannot suppose it. Tha's why I answered (E). The information give is just that a c b is a triangle...
 I think you can assume a line is straight if it's drawn straight. I can't recall the exact things you cannot assume in geometry as it's been a long time since I touched geometry. But I think the OG has a list of those items you can safely assume
Second point, I've learn in different GMAT DS tips, that for variables to be solved, there needs to be at least as much as equations as unknown. It doesn't seem to work if we consider following
 You're wrong on this one. In fact, for DS, having x number of variables does not mean you need x number of equations.
Anyway, for St1: we know c+d = 180, and so a = 45. However, we can't solve for b as we do not know c and we can't manipulate the variables to fit into the sum of angles for a triangle.
The most we can get via manipulation is
a+b+c = 180 45+b+180d = 180 bd = 45 > We still have two variables left.
However, with St 2:
You can easily write d = a+55 So c = 180a55 = 125a
a+b+c = 180 a+b+125a = 180 b = 55



VP
Joined: 29 Apr 2003
Posts: 1377

Answer wud be B...
Whats the OA?



Senior Manager
Joined: 08 Jun 2004
Posts: 486
Location: Europe

Definitely 'B'.
Nice question.



Director
Joined: 02 Mar 2006
Posts: 571
Location: France

OA is B.
Thanks Ywilfred for your explanation.
Concerning the solving of the equations (1) and (2), I totally understand and agree. But I was looking for a "shortcut" to answer such questions more quickly. If I knew after few seconds that in any DS involving equations that there have less or as much equations as variables, I could straight give an answer that we have( or not) enough information too answer.
So what should one think about such a statement taken out of Kaplan, in light of this DS triangle problem.
"Remember this matematical principle.Whatever number of different variables you need to solve for, you will need that same number of different equations relating at least one of those variables.
There are usually a few tough DS problems that can be made easy by applying this principle and the Kaplan Method for DS word problem. If you get such a problem, ask yoursel,' how many variables do I need to solve for? How many equations do I have?'"



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Re: In the figure above, what is the value of b? (1) a+c+d=225 [#permalink]
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12 Dec 2017, 19:31
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Re: In the figure above, what is the value of b? (1) a+c+d=225
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12 Dec 2017, 19:31






