OG11 Q89.... Do help

This topic has expert replies
User avatar
Master | Next Rank: 500 Posts
Posts: 218
Joined: Wed Dec 11, 2013 4:02 am
Thanked: 3 times
Followed by:4 members

OG11 Q89.... Do help

by [email protected] » Sun Mar 09, 2014 5:18 am
Image
OA A

User avatar
Master | Next Rank: 500 Posts
Posts: 218
Joined: Wed Dec 11, 2013 4:02 am
Thanked: 3 times
Followed by:4 members

by [email protected] » Sun Mar 09, 2014 5:24 am
I know the OA is right, but I can't eliminate the option E.
Give me a solid reason why " E" is wrong?

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sun Mar 09, 2014 2:30 pm
Networks of blood vessels in bats' wings serve only to disperse heat generated in flight. This heat is generated only because bats flap their wings. Thus paleontologists' recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis that Sandactylus flew by flapping its wings, not just by gliding.

The argument in the passage relies on which of the following assumptions?

(A) Sandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.

(B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.

(C) Winged dinosaurs that flaped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.

(D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.

(E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.
Premises:
The blood vessels in a bat's wings serve only one purpose: to disperse the heat generated by flapping.
The wings of Sandactylus had similar networks of blood vessels.
Conclusion:
Sandactylus must have flapped its wings.

The assumption is WHAT MUST BE TRUE for the conclusion to be valid.
Apply the NEGATION TEST.
When the correct answer choice is negated, the conclusion will be invalidated.

Answer choice A, negated:
Sandactylus would have had networks of blood vessels in the skin of its wings EVEN IF THESE NETWORKS WERE OF NO USE to Sandactylus.
If the networks of blood vessels were OF NO USE to Sandactylus, then the argument CANNOT conclude that these networks are evidence of wing-flapping.
Since the negation of A invalidates the conclusion, answer choice A is the necessary assumption: WHAT MUST BE TRUE for the conclusion to be valid.

The correct answer is A.

Answer choice E, negated:
Heat generated by Sandactylus in flapping its wings in flight could have been dispersed by something other than the blood vessels in its wings.
The negation of E suggests that Sandactylus could have dispersed the heat from wing-flapping in any number of ways, STRENGTHENING the conclusion that Sandactylus flapped its wings.
Since the negation of E does not invalidate the conclusion, eliminate E.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

User avatar
GMAT Instructor
Posts: 1052
Joined: Fri May 21, 2010 1:30 am
Thanked: 335 times
Followed by:98 members

by Patrick_GMATFix » Sun Mar 09, 2014 8:11 pm
Image

The answer is A. I go through the question in detail in the full solution below (taken from the GMATFix App).

Image

-Patrick
  • Ask me about tutoring.

User avatar
Master | Next Rank: 500 Posts
Posts: 218
Joined: Wed Dec 11, 2013 4:02 am
Thanked: 3 times
Followed by:4 members

by [email protected] » Tue Mar 11, 2014 6:42 am
Patrick!!
U rock \m/

Junior | Next Rank: 30 Posts
Posts: 25
Joined: Sun Sep 29, 2013 7:51 am

by swarnav999 » Fri Mar 14, 2014 8:57 am
I am unable to copy you Patrick. :/
Stil cannot eliminate E option. Guess I didnt understand your explanation.
Patrick_GMATFix wrote:Image

The answer is A. I go through the question in detail in the full solution below (taken from the GMATFix App).

Image

-Patrick

User avatar
GMAT Instructor
Posts: 1052
Joined: Fri May 21, 2010 1:30 am
Thanked: 335 times
Followed by:98 members

by Patrick_GMATFix » Fri Mar 14, 2014 11:06 am
I think the easiest way to eliminate E is to use the negation test. If you negate a real assumption, the conclusion will no longer make sense.

the argument uses the fact that a dinosaur had a network of blood vessels whose purpose was to disperse heat generated by wing flapping to conclude that since Sandactylus had similar blood vessels, it must have flown by flapping its wings.

The negated version of E: Heat generated by flapping wings could have been dispersed in other ways.

This has no impact on the argument. Maybe the heat could have been dispersed by a cooling water droplets as the bird flew through rainy clouds. So what? The author's argument remains unaffected; the dinosaur had these blood vessels because it flapped its wings, so since Sandactylus had similar blood vessels it must have flapped its wings also.

E cannot be an assumption because negating it does not cause the conclusion to fall apart.
  • Ask me about tutoring.