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Brent@GMATPrepNow
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IMO B
if yes I will post the sikn
vishu
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Triange in triangle
Source: Beat The GMAT — Data Sufficiency |
1) CB = 5.6
So we can find CD.
AC x CD = CB^2 ( put in a flash card )
we can find AD
AD = AC + CD
AD x CD = 7 X AB
so we can find AB - suf
2) CBD = 60, so we can find both CD and CB and the rest of the calculation is as in statement 1 , so SUF
I would choose D
It is a bad ass question!
So we can find CD.
AC x CD = CB^2 ( put in a flash card )
we can find AD
AD = AC + CD
AD x CD = 7 X AB
so we can find AB - suf
2) CBD = 60, so we can find both CD and CB and the rest of the calculation is as in statement 1 , so SUF
I would choose D
It is a bad ass question!
LGTCH
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"DON'T LET ANYONE STEAL YOUR DREAM!"
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"DON'T LET ANYONE STEAL YOUR DREAM!"
GMAT/MBA Expert
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Brent@GMATPrepNow
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Nice work, Logitech!
One important piece is to recognize that triangles ACB and BCD are similar triangles.
Check out my DS question (cars and students) - I'd love to see your assessment.
One important piece is to recognize that triangles ACB and BCD are similar triangles.
Check out my DS question (cars and students) - I'd love to see your assessment.
Brent Hanneson - Creator of GMATPrepNow.com
Brent, these are wonderful questions. I already checked the other question. Smart Smart Smart!! We are so lucky to have you here.Brent Hanneson wrote:Nice work, Logitech!
One important piece is to recognize that triangles ACB and BCD are similar triangles.
Check out my DS question (cars and students) - I'd love to see your assessment.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Hi Logitech,logitech wrote:1) CB = 5.6
So we can find CD.
AC x CD = CB^2 ( put in a flash card ) <<<-------???
we can find AD
AD = AC + CD
AD x CD = 7 X AB
so we can find AB - suf
2) CBD = 60, so we can find both CD and CB and the rest of the calculation is as in statement 1 , so SUF
I would choose D
It is a bad ass question!
Can u pls explain the theory behind this formula above ??
Thanks
Triangles ABD and BCD are similar, because:
1. Side BD is common to both
2. Angle BDC is common to both
3. Both are right angled triangles. i.e Angle ABD and Angle BCD are equal
hence we can write:
(BC/AB) = (BD/CD)
from (1): BC = 5.6
we can find out CD pythagores theorem.
so in the eqn (BC/AB) = (BD/CD), there is only one unknown, which is AB.
hence this is sufficient
from (2): angle CBD = 60 deg
so angle BDA = 30
hence the sides in triangle ABD are in ratio: root (3), 1 and 2
since we know one of the sides (BD = 7) we can find the other two.
hence this alone is sufficient too.
Ans is D
1. Side BD is common to both
2. Angle BDC is common to both
3. Both are right angled triangles. i.e Angle ABD and Angle BCD are equal
hence we can write:
(BC/AB) = (BD/CD)
from (1): BC = 5.6
we can find out CD pythagores theorem.
so in the eqn (BC/AB) = (BD/CD), there is only one unknown, which is AB.
hence this is sufficient
from (2): angle CBD = 60 deg
so angle BDA = 30
hence the sides in triangle ABD are in ratio: root (3), 1 and 2
since we know one of the sides (BD = 7) we can find the other two.
hence this alone is sufficient too.
Ans is D
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Ian Stewart
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The diagram in the question is actually related to one of the most famous diagrams in geometry - the one Euclid used to prove the Pythagorean Theorem. The early proofs of Pythagoras relied on the fact that you get three similar triangles when you draw, as in the diagram above, a height connecting the hypotenuse to the vertex with the 90 degree angle. Because we get similar triangles in such a picture, we really don't need much additional information to find all the lengths here, as logitech observed above. One other useful takeaway: it's generally worthwhile looking for similar triangles in any diagram where one triangle contains another, since when this happens, the two triangles are certain to share at least one angle.
My only suggestion, from a question design point of view, would be to remove the contradiction between the two statements - for example, to make Statement 1 read "CB = 3.5", so that it's logically possible to consider both statements together (using the first statement, each triangle is similar to a 3-4-5 triangle, while using the second, each triangle is a 30-60-90 triangle). Of course, the real GMAT always ensures the two statements are logically consistent.
My only suggestion, from a question design point of view, would be to remove the contradiction between the two statements - for example, to make Statement 1 read "CB = 3.5", so that it's logically possible to consider both statements together (using the first statement, each triangle is similar to a 3-4-5 triangle, while using the second, each triangle is a 30-60-90 triangle). Of course, the real GMAT always ensures the two statements are logically consistent.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com
ianstewartgmat.com
ianstewartgmat.com
GMAT/MBA Expert
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Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Location: Vancouver, BC
- Thanked: 5254 times
- GMAT Score:770
