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A compelling optical illusion called the illusion of velocity and size

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A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post Updated on: 06 Sep 2018, 21:27
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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

Originally posted by vksunder on 11 Jul 2008, 07:02.
Last edited by Bunuel on 06 Sep 2018, 21:27, edited 4 times in total.
Added OA.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 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.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 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.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 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.
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A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 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...
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 23 Sep 2012, 20:22
2
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 .

Does that help you ?
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post Updated on: 13 Apr 2013, 18:31
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.

Originally posted by margaretgmat on 13 Apr 2013, 17:39.
Last edited by margaretgmat on 13 Apr 2013, 18:31, edited 1 time in total.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 30 May 2013, 03:26
fozzzy wrote:
Can someone Please Explain? Is this an official question?


Yes this is an official question.

The OE states:

A If the truck is moving more slowly than the car, then the driver’s perception is accurate, and not affected by the optical illusion.
B Correct. This statement properly identifies an assumption implicit in the reasoning.
C If the truck is moving faster than the car, the motorist might judge that the two vehicles were moving at the same speed—or even that the truck was moving faster.
D It does not matter for which type of vehicle the driver’s estimate of lead time is more accurate; this assumption is not helpful in explaining the conclusion that the illusion makes larger objects appear to be moving more slowly than small objects.
E This contradicts information in the passage indicating that the larger the vehicle, the larger the distortion in the perceived speed.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 26 Aug 2013, 23:02
My analysis : illusion of velocity and size -> makes objects appear to move more slowly larger the objects are .

C : Motorcyclists estimate to cross the highway with a small car approaching is smaller then large truck approaching ...

Reason for conclusion to hold : Small car smaller size appears to move faster ( more velocity) , therefore smaller time required to cross it .

Large truck moves slowly ( less velocity ) more time to cross it .

Beyond this i am not able to get the assumption out of the argument ? Totally lost just choose B since the other option were all varying .
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 28 Aug 2013, 19:37
shelrod007 wrote:
My analysis : illusion of velocity and size -> makes objects appear to move more slowly larger the objects are .

C : Motorcyclists estimate to cross the highway with a small car approaching is smaller then large truck approaching ...

Reason for conclusion to hold : Small car smaller size appears to move faster ( more velocity) , therefore smaller time required to cross it .

Large truck moves slowly ( less velocity ) more time to cross it .

Beyond this i am not able to get the assumption out of the argument ? Totally lost just choose B since the other option were all varying .


Hi Shelrod,

You are almost correct in whatever you said. There is a minor gap in your understand that withholds you getting to the right assumption. Let's understand it.

Conclusion: Time for small car < time for large truck

Basis of conclusion: Larger the vehicle size, the slower it appears.

Right?

Now, if you understand the basis of the conclusion, it means that if a car and a truck both are moving at, say, 100 miles per hour (mph). Then, the following speeds may appear to a motorist:

Car: 100 mph
Truck: 95 mph

Therefore, when motorist estimates time for both car and truck, he would estimate a larger time for the truck because truck's speed is lower than car's.

Now, what if originally, the car was moving at 20mph and truck at 100mph. What would a motorist see?

He would see:

Car: 20mph
Truck: 95mph

Now, in this case, he would not estimate a longer time for the truck.

Do you get this?

For the motorist to estimate a lower time for the car, the car must be moving at the same or almost same speed as the truck. This is a required assumption for the conclusion to hold true.

Does it help?

Thanks,
Chiranjeev
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 27 Feb 2015, 08:31
Straight (B) without even reading other answer choices. The argument was talking about the illusion - so, if stated example should be an illusion the speed of both a car and a truck must be EQUAL. All other constellation it won't be an illusion, if there is a difference in speed.
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Re: A compelling optical illusion called the illusion of velocity and size  [#permalink]

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New post 13 Jul 2017, 05:30
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.

Assumption : Both of them are at same speed that is why the one if appearing to move slowly as compared to another because of the illusion. If it would have been opposite then, the illusion of velocity would have been different. Something has to be constant.

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

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Re: A compelling optical illusion called the illusion of velocity and size &nbs [#permalink] 06 Sep 2018, 19:02
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