# S2 QuestionWatch

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#1

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4 years ago
#2
I haven't got much time to look at this but it looks like conditional probability to me. What is the probability that A happens given B in this case you are after P(Lives 8 days given that it has lived 3) you know a formula to do these?
0
#3
(Original post by poorform)
I haven't got much time to look at this but it looks like conditional probability to me. What is the probability that A happens given B in this case you are after P(Lives 8 days given that it has lived 3) you know a formula to do these?
P(AnB)/P(B)

Struggling to get the numerator.
0
4 years ago
#4
(Original post by zed963)
P(AnB)/P(B)

Struggling to get the numerator.
Consider:

You have a formula for this no?
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#5
(Original post by poorform)
Consider:

You have a formula for this no?
No unfortunately, I've never come across this, I'm guessing this is from S1.
0
4 years ago
#6
(Original post by zed963)
No unfortunately, I've never come across this, I'm guessing this is from S1.
No this is given as part of the question.
0
4 years ago
#7
(Original post by zed963)
P(AnB)/P(B)

Struggling to get the numerator.
You are right with this formula. Reading the question it says GIVEN a mosquito survives 3 days, find the probability it will survive AT LEAST 5 MORE days
i.e P(T>8|T>3) = [P({T>8}n{T>3})]/P(t>3)

Consider the numerator. What is t>8 n t>3, thats like saying when are BOTH conditions satisfied, well both t>8 and t>3 are satisfied for t>8 so:

P(T>8|T>3) =[P(T>8)]/[P(T>3)]

In the question, it tells you the function for the probability that a mosquito survives more than t days (that is P(T>t)) so this can be used to put the fraction above into a numerical answer

Hope this helps somewhat..
1
#8
(Original post by Rjix)
You are right with this formula. Reading the question it says GIVEN a mosquito survives 3 days, find the probability it will survive AT LEAST 5 MORE days
i.e P(T>8|T>3) = [P({T>8}n{T>3})]/P(t>3)

Consider the numerator. What is t>8 n t>3, thats like saying when are BOTH conditions satisfied, well both t>8 and t>3 are satisfied for t>8 so:

P(T>8|T>3) =[P(T>8)]/[P(T>3)]

In the question, it tells you the function for the probability that a mosquito survives more than t days (that is P(T>t)) so this can be used to put the fraction above into a numerical answer

Hope this helps somewhat..
Wow, that makes sense thank you.
0
4 years ago
#9
(Original post by zed963)
Wow, that makes sense thank you.
No problem
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