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Math Help - 2 simple probability questions

  1. #1
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    2 simple probability questions

    Expected Grade E.G E.G E.G
    Studied More Than 4 Hours A B C D
    YES 0.12 0.06 0.12 0.02
    NO 0.13 0.21 0.26 0.08

    a) this student studied more than 4 hours and expects a B
    b) this student studied more than 4 hours or expects a B

    this is what i got:

    a) P=0.06
    b) P=0.32

    I thought question (a) was straightforward so I just assumed the probability would be same as the percentage of students thats studied more than 4 hours and expected a B which was 0.06

    For question (b) I got P=0.32 by simplying adding all the percentages of students that studied more than 4hours which was 0.32 and because within the 0.32 percentage the students who expected B were included, I'd assumed we just leave it at 0.32.

    ----------
    I just wanted to make sure if I answered them correctly, if not what did I do wrong :s

    Thanks in advance for reading and helping
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  2. #2
    MHF Contributor
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    Re: 2 simple probability questions

    Hey briankimmy.

    The first one is correct but the second is not.

    P(Studied for 4 hours OR Expects a B) = 0.12 + 0.06 + 0.12 + 0.02 + 0.21 in R gives:

    > 0.12 + 0.06 + 0.12 + 0.02 + 0.21
    [1] 0.53
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