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GMATFocus Q2 - probability

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frizo: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Thu Jan 22, 2009 10:19 am; Thanked: 1 times

GMATFocus Q2 - probability

by frizo » Wed Feb 11, 2009 9:57 pm

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?
.008
.128
.488
.512
.640
B

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Source: Beat The GMAT — Problem Solving | Wed Feb 11, 2009 9:57 pm

Bidisha800: Master | Next Rank: 500 Posts; Posts: 344; Joined: Sun Sep 28, 2008 11:00 am; Location: USA; Thanked: 6 times; Followed by:1 members

by Bidisha800 » Wed Feb 11, 2009 10:20 pm

probability = no rain X no rain X rain

=0.8*0.8*0.2
=0.128

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x2suresh: Master | Next Rank: 500 Posts; Posts: 258; Joined: Thu Aug 07, 2008 5:32 am; Thanked: 16 times

Re: GMATFocus Q2 - probability

by x2suresh » Wed Feb 11, 2009 10:21 pm

frizo wrote: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?
.008
.128
.488
.512
.640
B

= (prob that Saturday No rain)*(Prob that Sunday No rain)* Prob that Monday rain

= 0.8*0.8*0.2 = 0.128