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Probability Q

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by satish.nagdev » Fri Oct 30, 2009 9:43 pm
IMO C
(7C4)*(1/2^7)
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by punitkaur » Sat Oct 31, 2009 6:52 am
The answer is correct. Could you provide explanation please?

Thanks
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by satish.nagdev » Sat Oct 31, 2009 7:16 am
7C4 = number of combinations of days with rain and no rain say x=rainy day, y = non-rainy
so we can have a pattern xyxyxyx....
and probability for either case is 1/2 (50%) so for 7 days it will be 1/2*1/2...7 times = (1/2^7)

I came across other way to solve it using binomial probability distribution formula as well

P(f) = nCr * P(rainy day) * (1 - P(rainy day))^n-r
where n = 7 and r = 4 and P(rainy day) = 1/2
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by punitkaur » Sat Oct 31, 2009 7:50 am
Got it ... Thanks!!
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by life is a test » Sun Nov 01, 2009 6:31 am
satish.nagdev wrote:7C4 = number of combinations of days with rain and no rain say x=rainy day, y = non-rainy
so we can have a pattern xyxyxyx....
and probability for either case is 1/2 (50%) so for 7 days it will be 1/2*1/2...7 times = (1/2^7)

I came across other way to solve it using binomial probability distribution formula as well

P(f) = nCr * P(rainy day) * (1 - P(rainy day))^n-r
where n = 7 and r = 4 and P(rainy day) = 1/2
I misread the question to mean that it rains on 4 consecutive days out of the 7 - for this would the answer be 4C3 * 0.5^7?

thks.
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by fireplayer » Sun Nov 08, 2009 8:33 am
satish.nagdev

i agree with u
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by sanjana » Mon Nov 09, 2009 6:57 pm
Whenever an event has a 50% chance of occuring,it can always be treated as a flipping of a coin question.
This question is the same as "what is the probability of getting 4H on 7 flips of a coin"

You can apply the formula :
P(k results on n flips) = nck/2^n

Here,K=4,N=7 and the answer on substitution is 35/128.
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