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Edexcel S3---9/06/05 watch

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    (Original post by Spenceman_)
    Var [aX] = a2 Var [X]
    That sounds promising. I was trying to remember the rule - it would have helped if I got pen and paper out and to work from the definition.
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    lol mine is
    P1-100
    P2-94
    P3-91
    P4-86
    M1-95
    S1-75 >> retaking :p:
    good luck im gona try n get down to some more past papers
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    (Original post by Spenceman_)
    Just for the record I mean the following: -

    Var [3X] = 9 Var [X]

    BUT Var[X1 + X2 + X3 ] = 3 Var [X]

    ...because they are separate observations of the variable as opposed to one observation getting scaled.

    So say it said...time taken for a car to drive one mile is distributed X~ N(10,100)

    What's the probability it takes less then 35 minutes for a car to drive the three mile journey from here to school. You are dealing with X1 + X2 + X3 ~N(30,300) and not 3X ~ N(30,900).
    thts probably where i was confused
    thanx!
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    (Original post by Spenceman_)
    Just for the record I mean the following: -

    Var [3X] = 9 Var [X]

    BUT Var[X1 + X2 + X3 ] = 3 Var [X]

    ...because they are separate observations of the variable as opposed to one observation getting scaled.

    So say it said...time taken for a car to drive one mile is distributed X~ N(10,100)

    What's the probability it takes less then 35 minutes for a car to drive the three mile journey from here to school. You are dealing with X1 + X2 + X3 ~N(30,300) and not 3X ~ N(30,900).
    yeh for example if a question says the weight of a women follow a normal (8,10). 3 women go into a lift. What is the distribution of there weight it would be

    W~N(8+8+8,10+10+10)

    but if it said a woman goes into the lift whose weight is three times that of a normal woman then

    w~N(8+8+8, 9x10)
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    My P1 paper from last year contains the statement 5 x 2 = 20. Hmmm. It didn't deserve to be scaled to 100.
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    (Original post by hajira)
    lol mine is
    P1-100
    P2-94
    P3-91
    P4-86
    M1-95
    S1-75 >> retaking :p:
    good luck im gona try n get down to some more past papers
    me too

    good luck tmmrw!!
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    (Original post by BLUREMI)
    yeh for example if a question says the weight of a women follow a normal (8,10). 3 women go into a lift. What is the distribution of there weight it would be

    W~N(8+8+8,10+10+10)

    but if it said a woman goes into the lift whose weight is three times that of a normal woman then

    w~N(8+8+8, 9x10)
    ahh there goes my concern.. but its weird
    i hope im able to spot that!!
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    hajira do you have the mock s3 answers would be grateful if you could send it 2me
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    (Original post by kevins)
    hajira do you have the mock s3 answers would be grateful if you could send it 2me
    ahh.. i have the mark scheme for that but i jus came on the computer now! if u r around tell me ur email address n il send it
 
 
 
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Updated: June 9, 2005

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