Sta­tis­tics with Prob­a­bil­ity

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  • p-311 no-1
  • December 8, 2012 at 5:04 am #12945

    Afzal
    Participant

    i did this prob­lem but i think i did some thing wrong. can you point out the mis­take and how to draw it?

    no-1 page-311

    μ=128
    σ=16
    a. when n=9 then sd(xi)=16*√9=48, E[x]=9*128=1152
    b when n=25 then sd(xi)=16*√25=80, E[x]=25*128=3200
    c. when n=100 then sd(xi)=16*√100=160 E[x]=100*128=12800
    a.124< X >132
    124-1152132-1152
    -10028/48< (X-1152)/48>-1020/48
    -21.42-21.25
    =nor­mdist(-21.25)-=nor­mdist(-21.42)
    b..124132
    124-3200132-3200
    -3068/80<(X-3200)/80>-3068/80
    -38.45-38.35
    =nor­mdist(-38.35)-=nor­mdist(-38.45)
    c.
    124132
    124-12800132-12800
    -12676/160<(X-128)/160>-12668/160
    -79.23-79.18
    =nor­mdist(-79.18)-=nor­mdist(-79.23)

    December 16, 2012 at 11:35 pm #16194

    Ezra Halleck
    Participant

    Main prob­lem is that you are using the wrong for­mula. For the std dev of the sam­ple mean, you need to di­vide by the sqrt(n) and not mul­ti­ply.

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