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Probability - Help!!

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Junior | Next Rank: 30 Posts
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by agemroy » Fri Jul 11, 2008 7:41 am
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 3 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

Please explain..
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by VP_Jim » Fri Jul 11, 2008 8:42 am
If he were to return home on Monday, that means we had the following occur:

Saturday: No rain
Sunday: No rain
Monday Rain

So, we just need to multiply together the probabiltity of all those individual things:

80% chance of no rain on Saturday * 80% chance of no rain on Sunday * 20% chance of rain on Monday

.8*.8*.2 = .128, so the answer is B.
Jim S. | GMAT Instructor | Veritas Prep
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by sudhir3127 » Fri Jul 11, 2008 8:45 am
answer B ..

(probablity of no rain on sat)X(probablity of no rain on sun) X (probablity of rain on monday)

0.8*0.8*0.2= 0.128
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