Turn on thread page Beta
    • Thread Starter
    Offline

    14
    ReputationRep:
    So for the probability that 1 is less than and equal to X is less than equal to 4.

    I get:

    P(X<= 4) - P(X>=1)

    = P(X<= 4) - ( 1 - P (X < 1)

    But this is wrong and I don't know why.

    Why is it P(X <= 0) ?

    smh

    advice would be appreciated.
    Offline

    3
    ReputationRep:
    P(1<=X<=4) is P(X=1 or X=2 or X=3 or X=4)

    P(X<=4) is P(X=0 or X=1 or X=2 or X=3 or X=4)

    So P(1<=X<=4) = P(X<=4) - P(X=0)

    ( probability P(X=0) is the same as probability P(X<=0) since X can't be negative)
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by ludmila)
    P(1<=X<=4) is P(X=1 or X=2 or X=3 or X=4)

    P(X<=4) is P(X=0 or X=1 or X=2 or X=3 or X=4)

    So P(1<=X<=4) = P(X<=4) - P(X=0)

    ( probability P(X=0) is the same as probability P(X<=0) since X can't be negative)
    Thank you for your explanation. Since P(1 <= X) is the the same as the P ( X<1) = P(X=0).

    Is this correct, I see what you mean, thanks.
    Offline

    3
    ReputationRep:
    (Original post by Damien_Dalgaard)
    Thank you for your explanation. Since P(1 <= X) is the the same as the P ( X<1) = P(X=0).

    Is this correct, I see what you mean, thanks.
    P(1<=X) can't be the same as P(X<1).
    Always think what values X can have.
    P(1<=X) is the probability that X will be either 0 or 1.
    P(1<X) is the probability that X will be 0 only.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by ludmila)
    P(1<=X) can't be the same as P(X<1).
    Always think what values X can have.
    P(1<=X) is the probability that X will be either 0 or 1.
    P(1<X) is the probability that X will be 0 only.
    Sorry I meant to say P(1<=X) is the same as P(X>=1) which is the same as 1 - P(X <=1)

    Is that right?


    I am confused, if the probability of 1 is less than or equal to x, that must mean that x is greater than or equal to 1. Therefore the lowest value that will satisify that will be 1.

    Is this for discrete values only as well.

    Thank you for your reply.
    Offline

    3
    ReputationRep:
    (Original post by Damien_Dalgaard)
    Sorry I meant to say P(1<=X) is the same as P(X>=1) which is the same as 1 - P(X <=1)

    Is that right?


    I am confused, if the probability of 1 is less than or equal to x, that must mean that x is greater than or equal to 1. Therefore the lowest value that will satisify that will be 1.

    Is this for discrete values only as well.

    Thank you for your reply.
    OOOh, sorry, I didn't notice you used 1<=X (I always write is as X>=1 so didn't even think before I answered). Of course P(1<=X) is the same as P(X>=1) = 1 - P(X <1). But you can't say that P(1<=X<=4) = P(X<= 4) - P(X>=1).
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by ludmila)
    OOOh, sorry, I didn't notice you used 1<=X (I always write is as X>=1 so didn't even think before I answered). Of course P(1<=X) is the same as P(X>=1) = 1 - P(X <=1). But you can't say that P(1<=X<=4) = P(X<= 4) - P(X>=1).
    Sorry is it that (the part in bold).


    Right but from P(1<=X<=4) = P(X<= 4) - P(X>=1)

    Is it P(X<= 4) - ( 1 - (P X <= 1)

    So sorry to keep bothering you but this keeps frazzling me!
    Offline

    3
    ReputationRep:
    (Original post by Damien_Dalgaard)
    Sorry is it that (the part in bold).


    Right but from P(1<=X<=4) = P(X<= 4) - P(X>=1)

    Is it P(X<= 4) - ( 1 - (P X <= 1)

    So sorry to keep bothering you but this keeps frazzling me!
    That's all right

    a) P(X>=1) = 1 - P(X <1) (not
    P(X>=1) = 1 - P(X <=1) because you want to calculate probability when X is 1, 2, 3, .... By writing 1 - P(X <=1) you are excluding the option X=1.

    b) P(1<=X<=4) does NOT equal P(X<= 4) - P(X>=1).

    P(1<=X<=4) = P(X<= 4) - P(X<1) = P(X<=4) - P(X=0)
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by ludmila)
    That's all right

    a) P(X>=1) = 1 - P(X <1) (not P(X>=1) = 1 - P(X <=1) because you want to calculate probability when X is 1, 2, 3, .... By writing 1 - P(X <=1) you are excluding the option X=1.

    b) [/FONT][/FONT]
    P(1<=X<=4) = P(X<= 4) - P(X<1) = P(X<=4) - P(X=0)

    omg of course, I see it now.

    I've also done a number line and I can see it from there too.

    Thank you so much.

    Last last question this is for discrete probablities so applicable to binomial and poisson distribution, so we do not have to worry about the probability between 0 and 1 itself right.

    Are you doing S2/S3
    Offline

    3
    ReputationRep:
    (Original post by Damien_Dalgaard)
    omg of course, I see it now.

    I've also done a number line and I can see it from there too.

    Thank you so much.

    Last last question this is for discrete probablities so applicable to binomial and poisson distribution, so we do not have to worry about the probability between 0 and 1 itself right.

    Are you doing S2/S3
    No, you don't need to worry about decimals when dealing with discrete probabilities.

    I'm self-studying S1 and S2 (and the rest of the A level)
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by ludmila)
    No, you don't need to worry about decimals when dealing with discrete probabilities.

    I'm self-studying S1 and S2 (and the rest of the A level)

    Thought so thanks for the clarity, ah nice am self studying.

    s2
 
 
 

1,451

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should predicted grades be removed from the uni application process

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.