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If a grade was drawn at random from the data shown below, what is the probability that the grade is not a B?

Grade Frequency
A 2
B 8
C 11
D 2
F 1

I think it is 1 out of 5 or 4 but I am not sure? Please help :) Thank you much!

  • Math -

    There are 5 possible outcomes, one of which is a B.
    So what is P(B), and what is P(not B)?

    Hint : P(B) and P(not B) have to add up to 1.

  • Math -

    Oh ok I think I get it, so P(B)=0.5, 1/2,
    and P(not B)=0.5,1/2???
    Is that right?

  • Math -

    Sorry, not really.

    Figure out the probability of P(B) which is to get B out of 5 possible choices.

    The rest would be easy to figure out.

  • Math -

    Add up all the grades that aren't B's. Then put that over the total amount of grades.

  • Math -

    Ok so it would be P(B)=0.8, the probability that the grade is not a B.?

    I hope this is right now, if it isn't I give !

  • Math -

    Don't give up, you're right.... almost!

    What Jen showed you to do was
    P(not B), which equals 0.8
    ("...grades that aren't B's...")

    there is only one grade B, so it is 1/5, there are 4 grades that are not B, so
    P(not B)=4/5=0.8

    Sorry if it was too confusing, hope it's more clear now.

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