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# Easy probability

Author Message
Current Student
Joined: 29 Jan 2005
Posts: 5201

Kudos [?]: 437 [1], given: 0

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15 Nov 2007, 15:15
1
KUDOS
00:00

Difficulty:

(N/A)

Question Stats:

85% (00:52) correct 15% (00:56) wrong based on 323 sessions

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GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

Kudos [?]: 437 [1], given: 0

Manager
Joined: 08 Nov 2007
Posts: 97

Kudos [?]: 3 [1], given: 0

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15 Nov 2007, 15:26
1
KUDOS
GMAT TIGER wrote:
GMATT73 wrote:
GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

= 0.5^5
= close to 0.000

I make it D - 0.5 x 0.5 x 0.5 x 0.5 x 0.5 - which is 1/32 or closest to 0.31

Kudos [?]: 3 [1], given: 0

Manager
Joined: 26 Sep 2007
Posts: 65

Kudos [?]: 28 [1], given: 5

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15 Nov 2007, 15:26
1
KUDOS
D .031

probability of guessing it right = .5
So probability of guessing all 5 right = (.5)*(.5)*(.5)*(.5)*(.5) = .031

Kudos [?]: 28 [1], given: 5

Current Student
Joined: 29 Jan 2005
Posts: 5201

Kudos [?]: 437 [1], given: 0

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15 Nov 2007, 15:38
1
KUDOS

Kudos [?]: 437 [1], given: 0

CEO
Joined: 21 Jan 2007
Posts: 2734

Kudos [?]: 1076 [1], given: 4

Location: New York City

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21 Dec 2007, 07:46
1
KUDOS
pretty straightforward question.

binomial prob
p(hit) = p(miss) = .5 = 1/2

(1/2)^multiplier
(1/2)^5 = 1/32 = .03xxx

Kudos [?]: 1076 [1], given: 4

CEO
Joined: 29 Mar 2007
Posts: 2553

Kudos [?]: 528 [1], given: 0

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21 Dec 2007, 15:39
1
KUDOS
GMATT73 wrote:
GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

1/2^5 ---> 1/32 So D.

Kudos [?]: 528 [1], given: 0

Manager
Joined: 27 Oct 2008
Posts: 185

Kudos [?]: 166 [1], given: 3

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27 Sep 2009, 02:32
1
KUDOS
GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

Soln: (1/2) ^ 5 = 1/32 = .031

Kudos [?]: 166 [1], given: 3

CEO
Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2756

Kudos [?]: 1911 [1], given: 235

Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35

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30 Mar 2010, 07:18
1
KUDOS
bnagdev282 wrote:
whats wrong in this

P(missess none)
= 1-prob(missess all)
= 1- (1/32)
= 31/32

pls explain thks

You should have use this if they had asked he atleast got 1 right
then that P = 1-( P( no right) )

here it is asked he doesnt miss all
you have skipped the case when he missed 1,2,3,4 questions wrong.
p(1) = 1/2
p2 = 1/4
p3 = 1/8
p4 = 1/16 now subtract p1+p2+p3+p4 = 0.9375
from 31/32=0.96875
you will get p =0.03125
Hence D..... Do not down the cases you didnt considered .
Hope this helps.
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Kudos [?]: 1911 [1], given: 235

SVP
Joined: 29 Aug 2007
Posts: 2471

Kudos [?]: 856 [0], given: 19

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15 Nov 2007, 15:35
alrussell wrote:
GMAT TIGER wrote:
GMATT73 wrote:
GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

= 0.5^5
= close to 0.000

I make it D - 0.5 x 0.5 x 0.5 x 0.5 x 0.5 - which is 1/32 or closest to 0.31

yup yup agree with D. 0.031.

thought 0.5 to the power 5 would result in negligible value close to 0.

Kudos [?]: 856 [0], given: 19

Director
Joined: 03 Sep 2006
Posts: 864

Kudos [?]: 1106 [0], given: 33

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21 Dec 2007, 20:00
GMATT73 wrote:
GMATT randomly guesses the answers to a five-question true/false section on his stats final. If there is a 0.50 probability of making the correct choice on each question, then the probability that GMATT misses no questions is:

A) 0.000
B) 0.200
C) 0.500
D) 0.031

=0.5*0.5*0.5*0.5*0.5
=0.03125

Kudos [?]: 1106 [0], given: 33

Director
Joined: 25 Oct 2008
Posts: 594

Kudos [?]: 1182 [0], given: 100

Location: Kolkata,India

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24 Jul 2009, 19:15
1/32=D
_________________

http://gmatclub.com/forum/countdown-beginshas-ended-85483-40.html#p649902

Kudos [?]: 1182 [0], given: 100

Intern
Joined: 17 Jan 2010
Posts: 28

Kudos [?]: 4 [0], given: 3

Schools: SSE, LSE

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04 Mar 2010, 04:47
It´s great to work through this questions with all of you guys! It feels almost like a group work

Kudos [?]: 4 [0], given: 3

Intern
Joined: 09 Jan 2010
Posts: 27

Kudos [?]: 1 [0], given: 5

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30 Mar 2010, 03:48
whats wrong in this

P(missess none)
= 1-prob(missess all)
= 1- (1/32)
= 31/32

pls explain thks

Kudos [?]: 1 [0], given: 5

Manager
Joined: 08 Sep 2010
Posts: 159

Kudos [?]: 28 [0], given: 18

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18 Jun 2011, 07:03
0.5^5 = 1/32 = 0.031
ans D
_________________

My will shall shape the future. Whether I fail or succeed shall be no man's doing but my own.

If you like my explanations award kudos.

Kudos [?]: 28 [0], given: 18

Manager
Status: Essaying
Joined: 27 May 2010
Posts: 144

Kudos [?]: 9 [0], given: 8

Location: Ghana
Concentration: Finance, Finance
Schools: Cambridge
GMAT 1: 690 Q47 V37
GPA: 3.9
WE: Accounting (Education)

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28 Nov 2011, 09:08
Pro = (1/2)^5 = .031

Kudos [?]: 9 [0], given: 8

Non-Human User
Joined: 09 Sep 2013
Posts: 15632

Kudos [?]: 283 [0], given: 0

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22 May 2016, 08:40
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Kudos [?]: 283 [0], given: 0

Manager
Joined: 16 Mar 2016
Posts: 135

Kudos [?]: 43 [0], given: 0

Location: France
GMAT 1: 660 Q47 V33
GPA: 3.25

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22 May 2016, 08:46
Proba = $$\frac{1}{2^5}$$ = 1/32 = 0,03xxx

Kudos [?]: 43 [0], given: 0

Re: Easy probability   [#permalink] 22 May 2016, 08:46
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