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# PS - Q11

Author Message
Director
Joined: 27 Jun 2008
Posts: 526
WE 1: Investment Banking - 6yrs

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16 Sep 2008, 12:57
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Help me understand..

On Saturday morning, Malachi will begin a camping vacation and he will return home at
the end of the first day on which it rains. If on the first three days of the vacation the
probability of rain on each day is 0.2, what is the probability that Malachi will return
home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640
Senior Manager
Joined: 09 Oct 2007
Posts: 459

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16 Sep 2008, 21:32
Pawan,

the question basically asks what's the chance it wontrain for two consecutive days times the chance thay it will rain on the third day:

Chance of not raining: 1-0.2 = 0.8 (remember that posibility is measured 0 through 1)
Chance of raining: 0.2

Thus,
(0.8)(0.8)(0.2) = .128 = B
Director
Joined: 27 Jun 2008
Posts: 526
WE 1: Investment Banking - 6yrs

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17 Sep 2008, 07:11
OA is B

Thanks for the explaination, asdert!
VP
Joined: 17 Jun 2008
Posts: 1325

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17 Sep 2008, 10:49
pawan203 wrote:
Help me understand..

On Saturday morning, Malachi will begin a camping vacation and he will return home at
the end of the first day on which it rains. If on the first three days of the vacation the
probability of rain on each day is 0.2, what is the probability that Malachi will return
home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

prob of not raining (Sat) *prob of not raining(sun) *prob of raining (mon) =0.8*0.8*0.2=0.128
_________________

cheers
Its Now Or Never

Re: PS - Q11   [#permalink] 17 Sep 2008, 10:49
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