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# S2 question watch

1. how do you find something like P(10<=X<=13) from the tables and say if it was for poisson, not that it matters.

how would you do it generally?
2. (Original post by cooldudeman)
how do you find something like P(10<=X<=13) from the tables and say if it was for poisson, not that it matters.

how would you do it generally?

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3. (Original post by cooldudeman)
how do you find something like P(10<=X<=13) from the tables and say if it was for poisson, not that it matters.

how would you do it generally?
Firstly you need to be aware of whether the distribution is discrete or continuous. For a discrete distribution such as Poisson:

P(10<=X<=13) = P(X<=13) - P(X<=9). If you don't get it immediately you need to understand why this is. You can post back if you like.

For a continuous distribution, such as the normal distribution, it does not matter if the inequalities are strict or not, since P(X=10) = 0. Therefore you want:

P(10<=X<=13) = P(X<=13) - P(X<=10)
4. what if wit was P(a<=X<=b)? P(X<=b) - P(X<= a-1)?
5. (Original post by cooldudeman)
what if wit was P(a<=X<=b)? P(X<=b) - P(X<= a-1)?
You should read my other post as well. What you have written is correct for a discrete distribution such as Poisson as it can only take integer values. You'll also want to notice:

If you understand why you will be able to negotiate any question requiring use of the tables.
6. (Original post by metaltron)
You should read my other post as well. What you have written is correct for a discrete distribution such as Poisson as it can only take integer values. You'll also want to notice:

If you understand why you will be able to negotiate any question requiring use of the tables.
ok so the thing i wrote works for poisson and binomial distribution only since they are discrete?
so for the one you wrote the first part is, 10<X so X>10 so X>=11, 11<=X so P(11<=X<=13) so P(X<=13) - P(X<=11-1)?

if it was one of the ones you wrote for normal distribution, and the inequalities were not strict, would you just turn them to strict, and apply continuity correction and then the same method? like minusing 1 from the first part of the big inequality?
7. (Original post by cooldudeman)
ok so the thing i wrote works for poisson and binomial distribution only since they are discrete?
so for the one you wrote the first part is, 10<X so X>10 so X>=11, 11<=X so P(11<=X<=13) so P(X<=13) - P(X<=11-1)?

if it was one of the ones you wrote for normal distribution, and the inequalities were not strict, would you just turn them to strict, and apply continuity correction and then the same method? like minusing 1 from the first part of the big inequality?
You are correct for my previous example. For continuous distributions:

This is because you can include all values not just integers. Also:

8. (Original post by metaltron)
You are correct for my previous example. For continuous distributions:

This is because you can include all values not just integers. Also:

ok thanks
9. (Original post by metaltron)
You are correct for my previous example. For continuous distributions:

This is because you can include all values not just integers. Also:

Sorry to bring this topic up again but how do you deal with it for Z so normal distribution. Like
P (A <Z <-B) or if a was negative and b wasnt

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10. (Original post by cooldudeman)
Sorry to bring this topic up again but how do you deal with it for Z so normal distribution. Like
P (A <Z <-B) or if a was negative and b wasnt

Posted from TSR Mobile
First you standardise the normal distribution. Then you will treat it as a continuous distribution:

where a and b are positive.
11. (Original post by metaltron)
First you standardise the normal distribution. Then you will treat it as a continuous distribution:

where a and b are positive.
Oh yeah I get tgat. I was being stupid
Can you help with something else since no one is replying to my other thread. With continuous variables like rectangular and the other one thats in S2, how do you deal with conditional probability?
I imagine the standard formulas like P (X> 8 | X> 3)= P (X> 8) ÷ P (X> 3)
and this is when bith inequalities are more than. Is this true for all cases. I really cant do questions like these.

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