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A) 1/4 B) 1/3 C) 1/2 D) 2/3 E) 3/4

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Director
Joined: 22 Aug 2007
Posts: 566
A) 1/4 B) 1/3 C) 1/2 D) 2/3 E) 3/4 [#permalink]

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20 Sep 2007, 08:55
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A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4
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Senior Manager
Joined: 27 Aug 2007
Posts: 253

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20 Sep 2007, 09:26
A wild guess 1/4 but seems incorrect as it becomes too simple.

A

what is OA???
Director
Joined: 09 Aug 2006
Posts: 755

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20 Sep 2007, 09:36
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

I hate these kind of questions because they make me feel really dumb.

The light makes 3 revolutions in 60 seconds = 1 rev in 20 seconds assuming constant speed of revs.

Favorable outcome = 5 secs
Total outcome = 20 secs

Probability = 5/20 = 1/4.

Makes no sense and I have no clue how to do this. I would guess A in the exam and move the hell on!!!
Director
Joined: 22 Aug 2007
Posts: 566

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20 Sep 2007, 10:27
GK_Gmat wrote:
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

I hate these kind of questions because they make me feel really dumb.

The light makes 3 revolutions in 60 seconds = 1 rev in 20 seconds assuming constant speed of revs.

Favorable outcome = 5 secs
Total outcome = 20 secs

Probability = 5/20 = 1/4.

Makes no sense and I have no clue how to do this. I would guess A in the exam and move the hell on!!!

=))

sorry about the feelings, u r not alone...
nope, AO is different I will post it later, let`s see other explanations.
Director
Joined: 22 Aug 2007
Posts: 566

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20 Sep 2007, 10:29
Ferihere wrote:
A wild guess 1/4 but seems incorrect as it becomes too simple.

A

what is OA???

I made the same mistake. Will post OA later.
Director
Joined: 26 Jul 2007
Posts: 535
Schools: Stern, McCombs, Marshall, Wharton

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20 Sep 2007, 10:34
GK_Gmat wrote:
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

I hate these kind of questions because they make me feel really dumb.

The light makes 3 revolutions in 60 seconds = 1 rev in 20 seconds assuming constant speed of revs.

Favorable outcome = 5 secs
Total outcome = 20 secs

Probability = 5/20 = 1/4.

Makes no sense and I have no clue how to do this. I would guess A in the exam and move the hell on!!!

Isn't that the probability that you are IN the light and there for the probability that you are NOT is 1 - 1/4 or 3/4

Another way of looking at it:

You are standing on the circumference of a circle. The light will cover the entire circumference in 20 seconds therefore it will only cover 25% in 5 seconds. That leaves 75% of the circumference that you could be standing on and remain in the dark.
Director
Joined: 22 Aug 2007
Posts: 566

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20 Sep 2007, 11:07
gixxer1000 wrote:
GK_Gmat wrote:
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

I hate these kind of questions because they make me feel really dumb.

The light makes 3 revolutions in 60 seconds = 1 rev in 20 seconds assuming constant speed of revs.

Favorable outcome = 5 secs
Total outcome = 20 secs

Probability = 5/20 = 1/4.

Makes no sense and I have no clue how to do this. I would guess A in the exam and move the hell on!!!

Isn't that the probability that you are IN the light and there for the probability that you are NOT is 1 - 1/4 or 3/4

Another way of looking at it:

You are standing on the circumference of a circle. The light will cover the entire circumference in 20 seconds therefore it will only cover 25% in 5 seconds. That leaves 75% of the circumference that you could be standing on and remain in the dark.

AO is E,

thank you for your explanation, clear now.
Senior Manager
Joined: 13 Mar 2007
Posts: 294
Location: Russia, Moscow

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20 Sep 2007, 11:19
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

GMATClub challenges rules!!!
Director
Joined: 11 Jun 2007
Posts: 914

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20 Sep 2007, 15:41
IrinaOK wrote:
A) 1/4
B) 1/3
C) 1/2
D) 2/3
E) 3/4

yay!!! i had gotten 3/4 (E)
Re: Probability_dark   [#permalink] 20 Sep 2007, 15:41
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