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The probability of success in a field event is the ninth part of the

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Intern
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The probability of success in a field event is the ninth part of the  [#permalink]

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New post 16 Apr 2018, 05:57
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A
B
C
D
E

Difficulty:

  75% (hard)

Question Stats:

20% (01:12) correct 80% (00:55) wrong based on 10 sessions

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The probability of success in a field event is the ninth part of the probability of failure. Successive and independent trials are held until success occurs for the first time. In these circumstances, the expected number of failures that should occur until the first success occurs is equal to:

(A) 2
(B) 3
(C) 6
(D) 9
(E) 10

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Prof Marcelo Roseira
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GMAT Prep Online
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Twitter: @cursofdx
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Posts: 94
Location: India
Concentration: General Management, Leadership
Schools: ISB '19, IIMB
GMAT 1: 580 Q43 V27
GMAT 2: 650 Q32 V48
GRE 1: Q160 V151
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WE: Design (Consulting)
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The probability of success in a field event is the ninth part of the  [#permalink]

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New post 16 Apr 2018, 06:13
1
CursoFDX wrote:
The probability of success in a field event is the ninth part of the probability of failure. Successive and independent trials are held until success occurs for the first time. In these circumstances, the expected number of failures that should occur until the first success occurs is equal to:

(A) 2
(B) 3
(C) 6
(D) 9
(E) 10


From the question stem, we understand that, probability of success P(s) is 1/9 of probability of failure P(f).
P(s) = 1/9 P(f).
Now analyzing from the point of view of options, if the number of trials before first success is 2 then P(s) =1/2 and P(f) = 1/2 (Wrong, Not what question stem mentions)
From option B, P(s) = 1/3, P(f) = 2/3, (Wrong, question stem needs P(s) = 1/9P(f)
from option C, P(s) = 1/6, P(f) = 5/6. (Wrong)
From option D , P(s) = 1/9, P(f) = 8/9 (Wrong)
From option E, P(s) = 1/10, P(f) = 9/10 => P(s)/P(f) = 1/9 => P(s)=1/9 P(f) (Right Answer)
Hence option E is right answer
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WE: Marketing (Telecommunications)
Re: The probability of success in a field event is the ninth part of the  [#permalink]

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New post 16 Apr 2018, 06:23
CursoFDX wrote:
The probability of success in a field event is the ninth part of the probability of failure. Successive and independent trials are held until success occurs for the first time. In these circumstances, the expected number of failures that should occur until the first success occurs is equal to:

(A) 2
(B) 3
(C) 6
(D) 9
(E) 10


Let Failure = x, so Success= x/9. Since S+F=1 --> x + x/9 = 1 --> F=9/10 and S=1/10

{9F}+{1S}=10. I got max 9 Failures before 1 Success, why 10 F (E)? The Q asks how many F not trials why 10 and not 9???
Thanks.
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Re: The probability of success in a field event is the ninth part of the  [#permalink]

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New post 19 Apr 2018, 17:55
1
That is the problem. I also marked letter (D). I think that official answer (E) is wrong.

Hero8888 wrote:
CursoFDX wrote:
The probability of success in a field event is the ninth part of the probability of failure. Successive and independent trials are held until success occurs for the first time. In these circumstances, the expected number of failures that should occur until the first success occurs is equal to:

(A) 2
(B) 3
(C) 6
(D) 9
(E) 10


Let Failure = x, so Success= x/9. Since S+F=1 --> x + x/9 = 1 --> F=9/10 and S=1/10

{9F}+{1S}=10. I got max 9 Failures before 1 Success, why 10 F (E)? The Q asks how many F not trials why 10 and not 9???
Thanks.

_________________

Prof Marcelo Roseira
Curso FDX
GMAT Prep Online
Brazil
Twitter: @cursofdx
Instagram: @cursofdx
Skype: fdx.anpad

GMAT Club Bot
Re: The probability of success in a field event is the ninth part of the &nbs [#permalink] 19 Apr 2018, 17:55
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