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# If John was on a camping trip (starting on Saturday) and

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Director
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If John was on a camping trip (starting on Saturday) and [#permalink]  03 Dec 2003, 17:48
If John was on a camping trip (starting on Saturday) and would leave if it rained. Would he go home on Monday? There's a 20% chance of raining each day.
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Re: prob. of raining [#permalink]  03 Dec 2003, 18:29
dj wrote:
If John was on a camping trip (starting on Saturday) and would leave if it rained. Would he go home on Monday? There's a 20% chance of raining each day.

0.8*0.8*0.2=0.128, right?
Manager
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I am assuming that since the question asks if he will leave on Monday, we're not worried about Sat. or Sun. and thus there is an 80% chance he will not go home Sat., 80% chance he will not go home on Sun., and a 20% he will leave on Monday.

Is this correct logic?

Thanks,
CJ
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why it cannot be 0.8*0.8*0.8
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because it's the probability that he would "leave" on monday and not that he would "stay" on monday. Therefore, you have to take into account the probability on the 3rd day that it is raining (20%), so that he would leave on that day
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just out of curiosity, if you changed the question to say, what is the probability that he will leave BY Monday. would it be 60%

.2+.2+.2?
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just out of curiosity, if you changed the question to say, what is the probability that he will leave BY Monday. would it be 60%

.2+.2+.2?
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duncan wrote:
just out of curiosity, if you changed the question to say, what is the probability that he will leave BY Monday. would it be 60%

.2+.2+.2?

Nope.

.2+.2*.8+.8*.8*.2=.488

Just to check, let's do it the other way around:

1-0.8*.8*.8=.488

Please correct me if I am wrong
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