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# Help with S2 question!!

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2. Attachment 558291558293
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3. Probability is 0.8. Look at poisson tables for 0.8 where P(X<<1) = 0.8. Find the Y
4. It's a good idea to write down what you're distribution is. You want X to be "the number of emissions in 4 seconds", you know there is 1 per second, so in 4 seconds there's going to be 4. So X~po(4)

I'm not sure what you've done there, but the poisson distribution formula is
5. (Original post by Teleport1)
Probability is 0.8. Look at poisson tables for 0.8 where P(X<<1) = 0.8. Find the Y
0.8 isn't in the tables
6. (Original post by NotNotBatman)
It's a good idea to write down what you're distribution is. You want X to be "the number of emissions in 4 seconds", you know there is 1 per second, so in 4 seconds there's going to be 4. So X~po(4)

I'm not sure what you've done there, but the poisson distribution formula is
I used used the formula for P(X=0) and P(X=1) then added them which would equal 0.8?
7. (Original post by swagmister)
I used used the formula for P(X=0) and P(X=1) then added them which would equal 0.8?
then divide by 4
8. (Original post by Teleport1)
then divide by 4
Divide P(X=0)+P(X=1) by 4 before making it equal 0.8?
9. (Original post by swagmister)
Divide P(X=0)+P(X=1) by 4 before making it equal 0.8?
The above answer shouldnt be the right answer. Something is messed up. Try putting the given Y answer back into the formula to see if you get 0.8 which you shouldnt
10. (Original post by Teleport1)
The above answer shouldnt be the right answer. Something is messed up. Try putting the given Y answer back into the formula to see if you get 0.8 which you shouldnt
Yep dividing P(X<<1) by 4 gives an imaginary number. I'm not sure where I've gone wrong with the working out I've shown
11. (Original post by swagmister)
Yep dividing P(X<<1) by 4 gives an imaginary number. I'm not sure where I've gone wrong with the working out I've shown
No i mean the answer of 0.206 is wrong. If you try to work backwards by putting it into the formula with x=1, it doesnt give anything close to 0.8 whether you divide/multiply by 4 or not. So their answer is most likely wrong
12. (Original post by Teleport1)
No i mean the answer of 0.206 is wrong. If you try to work backwards by putting it into the formula with x=1, it doesnt give anything close to 0.8 whether you divide/multiply by 4 or not. So their answer is most likely wrong
It does give 0.8 because you have to times 0.206 by 4 as the probability of 0 and 1 was for 4 seconds
13. I didn't see that the emission rate changes, what you have done is right up to the third line, but you can't take natural logs to one term, it must be all of it. I would suggest multiplying through by , but then you get an equation with a term as well, which I can only think of solving right now by iterative methods. It is 0.824... , then just divide it by 4.
14. (Original post by NotNotBatman)
I didn't see that the emission rate changes, what you have done is right up to the third line, but you can't take natural logs to one term, it must be all of it. I would suggest multiplying through by , but then you get an equation with a term as well, which I can only think of solving right now by iterative methods. It is 0.824... , then just divide it by 4.
Oh right I'm still not sure how I would go about solving it though
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