Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 29 May 2017, 12:50

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# A compelling optical illusion called the illusion of

Author Message
TAGS:

### Hide Tags

Senior Manager
Joined: 10 Mar 2008
Posts: 361
Followers: 5

Kudos [?]: 291 [1] , given: 0

A compelling optical illusion called the illusion of [#permalink]

### Show Tags

11 Jul 2008, 07:02
1
KUDOS
12
This post was
BOOKMARKED
00:00

Difficulty:

15% (low)

Question Stats:

75% (02:17) correct 25% (01:31) wrong based on 818 sessions

### HideShow timer Statistics

Official Guide for GMAT Verbal Review, 2nd Edition

Practice Question
Question No.: 76
Page: 143
Difficulty:

A compelling optical illusion called the illusion of velocity and size makes objects appear to be moving more slowly the larger the objects are. Therefore, a motorist’s estimate of the time available for crossing a highway with a small car approaching is bound to be lower than it would be with a large truck approaching.

The conclusion above would be more properly drawn if it were made clear that the

(A) truck’s speed is assumed to be lower than the car’s
(B) truck’s speed is assumed to be the same as the car’s
(C) truck’s speed is assumed to be higher than the car’s
(D) motorist’s estimate of time available is assumed to be more accurate with cars approaching than with trucks approaching
(E) motorist’s estimate of time available is assumed to be more accurate with trucks approaching than with cars approaching
[Reveal] Spoiler: OA

Last edited by mau5 on 17 Oct 2013, 13:42, edited 3 times in total.
If you have any questions
New!
Director
Joined: 10 Sep 2007
Posts: 943
Followers: 8

Kudos [?]: 303 [0], given: 0

### Show Tags

11 Jul 2008, 07:14
IMO B.
Truck is heavier, so if car and truck run at same speed, truck will appear slower. Therefore driver from opposite side will estimate that car will quickly cross as compared to truck.
Manager
Joined: 02 May 2008
Posts: 87
Followers: 1

Kudos [?]: 174 [0], given: 0

### Show Tags

11 Jul 2008, 07:36
Ans : B.
In all the other cases the conclusion drawn may not be true.
Lets say option A was true.
In this case since the truck is slower than the car it will in any case take more time to reach the motorists irrespective of other factors like illusion of velocity or size.
Director
Joined: 25 Oct 2006
Posts: 640
Followers: 14

Kudos [?]: 558 [0], given: 6

### Show Tags

11 Jul 2008, 08:58
Premise: due to illusion - object size makes objects appear to be moving more
slowly.
Conclusion: time to cross car is less than time to cross truck. Hence Car takes less time while truch takes more time to cover the distance.

A. if truck's speed is less, it is not illusion - Can not be the answer
B. If speeds are same, illusion acts - Answer
C. again Speed should be constant
D and E: Accuracy of Motorist's estimation is not be considered as we are making relation between illusion and time while speed is contant.
_________________

If You're Not Living On The Edge, You're Taking Up Too Much Space

Senior Manager
Status: MBAing!!!!
Joined: 24 Jun 2011
Posts: 297
Location: United States (FL)
Concentration: Finance, Real Estate
GPA: 3.65
WE: Project Management (Real Estate)
Followers: 6

Kudos [?]: 52 [0], given: 56

### Show Tags

26 Oct 2011, 12:57
I picked B...that is the correct assumption to arrive to that conclusion.
Intern
Joined: 27 Jan 2011
Posts: 28
Followers: 0

Kudos [?]: 9 [0], given: 0

### Show Tags

27 Oct 2011, 14:50
"B". Assumption has to be tied to the premise (illusion) to arrive at the conclusion.
Manager
Joined: 11 Jul 2009
Posts: 167
WE: Design (Computer Software)
Followers: 1

Kudos [?]: 52 [0], given: 69

### Show Tags

28 Oct 2011, 04:19
B..
_________________

Kaustubh

BSchool Forum Moderator
Status: Flying over the cloud!
Joined: 17 Aug 2011
Posts: 887
Location: Viet Nam
GMAT Date: 06-06-2014
GPA: 3.07
Followers: 74

Kudos [?]: 658 [0], given: 44

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

16 Dec 2011, 03:34
B
_________________

Rules for posting in verbal gmat forum, read it before posting anything in verbal forum
Giving me + 1 kudos if my post is valuable with you

The more you like my post, the more you share to other's need

CR: Focus of the Week: Must be True Question

Manager
Joined: 07 Aug 2011
Posts: 181
Location: United States
GMAT 1: 690 Q48 V37
Followers: 3

Kudos [?]: 23 [0], given: 6

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

26 Dec 2011, 11:46
B
Manager
Joined: 28 Sep 2011
Posts: 200
Followers: 1

Kudos [?]: 72 [0], given: 5

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

24 Mar 2012, 18:36
I have chosen B for this question:

The optical illusion is only true if the 2 objects are moving at the same speed.

A. This is not an assumption made by the argument. If the truck's speed is slower, then what is the point of the optical illusion? Clearly, if the truck is moving slower, the motorist will have more time.

B. This is the correct answer. We have a good comparison now because we are comparing 2 objects moving at the same speed, so the larger truck will appear to be moving slower than the small car.

C. Same as A but reversed

D. How can we assume this? Nothing in the passage mentions the motorist's ability to estimate time.

E. Same as E.
Manager
Joined: 03 Aug 2011
Posts: 54
Followers: 1

Kudos [?]: 5 [0], given: 3

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

25 Mar 2012, 02:14

because only if we assume, both of the vehicles move at the same speed, we can make the conclusion valid.
Intern
Joined: 10 Dec 2011
Posts: 42
Location: India
Concentration: Finance, Economics
GMAT Date: 09-28-2012
WE: Accounting (Manufacturing)
Followers: 0

Kudos [?]: 15 [0], given: 4

A compelling optical illusion called the illusion of [#permalink]

### Show Tags

22 Sep 2012, 14:02
A compelling optical illusion called the illusion of velocity and size makes objects appear to be moving more
slowly the larger the objects are. Therefore, a motorist’s estimate of the time available for crossing a highway
with a small car approaching is bound to be lower than it would be with a large truck approaching.
The conclusion above would be more properly drawn if it were made clear that the
(A) truck’s speed is assumed to be lower than the car’s
(B) truck’s speed is assumed to be the same as the car’s
(C) truck’s speed is assumed to be higher than the car’s
(D) motorist’s estimate of time available is assumed to be more accurate with cars approaching than with trucks
approaching
(E) motorist’s estimate of time available is assumed to be more accurate with trucks approaching than with cars
approaching

(My only query - Read this after doing the Q why cannot the answer be D?. There are two things. First, either his estimate about cars is accurate (which should be if we have to prove that he has this optical illusion concerning large objects. Second, his estimate about cars is more accurate than trucks - which might mean that both his estimates are incorrect, hence he has optical illusion concerning large and small objects. Then this answer might not make sense??? --- please guide...
Joined: 28 May 2012
Posts: 137
Location: India
Concentration: General Management, Strategy
GPA: 3.33
WE: Information Technology (Retail)
Followers: 3

Kudos [?]: 67 [1] , given: 11

### Show Tags

23 Sep 2012, 20:22
1
KUDOS
talismaaniac wrote:
A compelling optical illusion called the illusion of velocity and size makes objects appear to be moving more
slowly the larger the objects are. Therefore, a motorist’s estimate of the time available for crossing a highway
with a small car approaching is bound to be lower than it would be with a large truck approaching.
The conclusion above would be more properly drawn if it were made clear that the
(A) truck’s speed is assumed to be lower than the car’s
(B) truck’s speed is assumed to be the same as the car’s
(C) truck’s speed is assumed to be higher than the car’s
(D) motorist’s estimate of time available is assumed to be more accurate with cars approaching than with trucks
approaching
(E) motorist’s estimate of time available is assumed to be more accurate with trucks approaching than with cars
approaching

(My only query - Read this after doing the Q why cannot the answer be D?. There are two things. First, either his estimate about cars is accurate (which should be if we have to prove that he has this optical illusion concerning large objects. Second, his estimate about cars is more accurate than trucks - which might mean that both his estimates are incorrect, hence he has optical illusion concerning large and small objects. Then this answer might not make sense??? --- please guide...

I could not really get your statement, however, I don't think the accuracy of time is really important in this question.

The premise already says that [b]larger objects tend to appear to be moving slowly.[/b] . You have to take this at Face value .

So if the truck and the car are moving at the same speed , only then will the motorist estimate that the truck is a large object and hence, he estimates it to be moving slowly.
That said, if they are at the same speed , the vehicles' weight then come into picture.

Larger objects -> slowly
Smaller objects -> faster .

_________________

You want something, go get it . Period !

Director
Affiliations: SAE
Joined: 11 Jul 2012
Posts: 508
Location: India
Concentration: Strategy, Social Entrepreneurship
GMAT 1: 710 Q49 V37
GPA: 3.5
WE: Project Management (Energy and Utilities)
Followers: 44

Kudos [?]: 289 [0], given: 269

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

24 Sep 2012, 22:00
I agree with Ankit.

The illusion is a function of two Variables
1 – Speed
2 – Size

We know that truck is bigger than the car but we do not about the speed. So, to arrive at a conclusion we need the second variable i.e. the Speed

_________________

First Attempt 710 - http://gmatclub.com/forum/first-attempt-141273.html

Director
Joined: 03 Aug 2012
Posts: 894
Concentration: General Management, General Management
GMAT 1: 630 Q47 V29
GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)
Followers: 24

Kudos [?]: 769 [0], given: 322

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

20 Feb 2013, 23:28
This is classic example of Assumption question where we need not put Math knowledge in the POE.

we have to assume other things being equal , optical illusion is justified for the time(car) <time(truck)

Hope that helps !!
_________________

Rgds,
TGC!
_____________________________________________________________________
I Assisted You => KUDOS Please
_____________________________________________________________________________

Current Student
Status: MBA Candidate, Class of 2017
Affiliations: SMU Cox
Joined: 24 Sep 2012
Posts: 195
Location: United States (TX)
Concentration: General Management, Strategy
GMAT 1: 710 Q48 V39
GPA: 3.75
WE: Project Management (Energy and Utilities)
Followers: 7

Kudos [?]: 65 [0], given: 31

Re: RE: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

21 Feb 2013, 01:12

Sent from my Lumia 800 using Board Express
_________________

My GMAT debrief

greatness is not about possessing talent but about having the discipline to summon that talent whenever needed!!!

Please Kudos my post if it helped you!!

VP
Joined: 09 Jun 2010
Posts: 1394
Followers: 5

Kudos [?]: 130 [0], given: 862

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

21 Feb 2013, 03:34
I prethink an assumption before going to answer choices.

my prethinking: motorist is affected by ilusion.

clearly, this prethought assumption is different from the assumption in oa. but when I read b, I immediately realize this assumption.

the prethinking process help us better understand the argument because we already know one assumption. the point is that it is easier to realize a new assumption (in oa) when we already know an assumption which we prethink.

I think this point is important.

pls comment on my thinking.
_________________

visit my facebook to help me.
on facebook, my name is: thang thang thang

Senior Manager
Status: Making every effort to create original content for you!!
Joined: 23 Dec 2010
Posts: 484
Location: United States
Concentration: Healthcare, Social Entrepreneurship
GMAT 1: 660 Q48 V34
GMAT 2: 750 Q49 V42
Followers: 363

Kudos [?]: 2030 [0], given: 82

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

21 Feb 2013, 03:43
thangvietnam wrote:
I prethink an assumption before going to answer choices.

my prethinking: motorist is affected by ilusion.

clearly, this prethought assumption is different from the assumption in oa. but when I read b, I immediately realize this assumption.

the prethinking process help us better understand the argument because we already know one assumption. the point is that it is easier to realize a new assumption (in oa) when we already know an assumption which we prethink.

I think this point is important.

pls comment on my thinking.

Hi thangvietnam,

Yes you are right, the importance of prethinking is to understand the argument before you jump into the answer choice. Even if you do not get the correct answer choice, you have a solid understanding of the argument before you attack the answer choices.

Vercules
_________________

Intern
Joined: 05 Mar 2013
Posts: 14
GMAT Date: 04-20-2013
Followers: 0

Kudos [?]: 4 [0], given: 9

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

13 Apr 2013, 17:39
Blue Book CR67

Strengthen
Conclusion: Estimated that small car takes LESS time than large truck. Why?
Premise: (On the basis of illusion of v and s) Appeared that larger objects to have less speed, thus incurred more time.

Not A: If assumed that truck's speed less than car, then estimation is not necessary since the case presents that it must always be true that car will take LESS time.
It's B: If assumed that truck's speed is same as car (holding all other factors, in this case is velocity, constant), this is in accordance with the illusion theory that the estimation is based on the appearance that car takes LESS time than large truck.

Last edited by margaretgmat on 13 Apr 2013, 18:31, edited 1 time in total.
Manager
Status: Looking to improve
Joined: 15 Jan 2013
Posts: 175
GMAT 1: 530 Q43 V20
GMAT 2: 560 Q42 V25
GMAT 3: 650 Q48 V31
Followers: 1

Kudos [?]: 67 [0], given: 65

Re: A compelling optical illusion called the illusion of [#permalink]

### Show Tags

13 Apr 2013, 18:14

This question type is a find the assumption, which must be true otherwise the conclusion falls apart. The conclusion is motor estimate when looking at small car is smaller than when looking at bigger truck and this is because of optical illusion.

B is the only answer which destroys the conclusion if negated - The speed of approaching car and truck are not the same..

//kudos please, if this explanation is good.
_________________

KUDOS is a way to say Thank You

Re: A compelling optical illusion called the illusion of   [#permalink] 13 Apr 2013, 18:14

Go to page    1   2    Next  [ 27 posts ]

Similar topics Replies Last post
Similar
Topics:
2 One of the effects of lead poisoning is an inflammation of the optic 5 02 Jan 2015, 11:04
35 Editorial: In a compelling preponderance of clinical trials, 29 19 Apr 2016, 13:42
6 Existing optical lenses are not thin or flat enough to 12 11 Apr 2016, 14:10
2 Existing optical lenses are not thin or flat enough to 7 11 Apr 2016, 14:08
4 Calling MGMAT instructors for HELP. 12 19 Feb 2017, 04:53
Display posts from previous: Sort by