Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    17
    ReputationRep:
    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?
    Offline

    1
    ReputationRep:
    (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?
    P(X \leq 13) - P(X \leq 9)


    Posted from TSR Mobile
    Offline

    10
    ReputationRep:
    (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)
    • Thread Starter
    Offline

    17
    ReputationRep:
    what if wit was P(a<=X<=b)? P(X<=b) - P(X<= a-1)?
    Offline

    10
    ReputationRep:
    (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:

     P(10&lt;X \leq 13) = P(X \leq 13) - P(X \leq 10)

    If you understand why you will be able to negotiate any question requiring use of the tables.
    • Thread Starter
    Offline

    17
    ReputationRep:
    (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:

     P(10&lt;X \leq 13) = P(X \leq 13) - P(X \leq 10)

    If you understand why you will be able to negotiate any question requiring use of the tables.
    sorry, just read your posts now.
    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?
    Offline

    10
    ReputationRep:
    (Original post by cooldudeman)
    sorry, just read your posts now.
    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:

     P(10 \leq X \leq 13) = P(10 &lt; X &lt; 13) = P(X \leq 13) - P(X \leq 10)

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

     P(X=10) = P(X=13) = 0
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by metaltron)
    You are correct for my previous example. For continuous distributions:

     P(10 \leq X \leq 13) = P(10 &lt; X &lt; 13) = P(X \leq 13) - P(X \leq 10)

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

     P(X=10) = P(X=13) = 0
    ok thanks
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by metaltron)
    You are correct for my previous example. For continuous distributions:

     P(10 \leq X \leq 13) = P(10 &lt; X &lt; 13) = P(X \leq 13) - P(X \leq 10)

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

     P(X=10) = P(X=13) = 0
    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
    Offline

    10
    ReputationRep:
    (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:

     P(a &gt; X &gt; -b)  = P(X \leq a) - P(X \leq -b) = P(X \leq a) - (1 - P(X \leq b))

    where a and b are positive.
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by metaltron)
    First you standardise the normal distribution. Then you will treat it as a continuous distribution:

     P(a &gt; X &gt; -b)  = P(X \leq a) - P(X \leq -b) = P(X \leq a) - (1 - P(X \leq b))

    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.

    Posted from TSR Mobile
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.