Statisitics

In a large section of a Chemistry class, the points for the final exam are normally distributed, with a mean of 72, and a variance of 81. Grades are to be assigned according to the following rule: the top 10% receive As, the next 20% receive Bs, the middle 40% receive Cs, the next 20% receive Ds, and the bottom 10% receive Fs. Find the lowest score on the final exam that would qualify a student for an A, a B, a C, and a D.

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  1. P((x-72)/9)=90%
    (x-72)/9=1.28 [normal distribution table]

    x=83.52
    83.52 at least for getting A

    P((x-72)/81)=10%
    (x-72)/81=-1.28 [normal distribution table]

    x=60.48
    60.48 maximum for getting D

    for B, score is between 72 and 83.52

    for C, score is between 60.48 and 72

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