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Math Help - Probability Help

  1. #1
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    Probability Help

    The daily sale of lunch is a random variable. Let us call it X. X ~ N (70,9). What is the probability that in a given day the restaurant sells more than 75 lunches?

    Is this telling me that the population average is 70 lunches with variance of 9?
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  2. #2
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    So this is what I came up with, please tell me if I'm wrong...
    P(x>75)=
    P(z>(75-70)/3)=
    P(z>1.68)=
    0.0465
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  3. #3
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    Quote Originally Posted by FGCUguy View Post
    So this is what I came up with, please tell me if I'm wrong...
    P(x>75)=
    P(z>(75-70)/3)=
    P(z>1.68)=
    0.0465
    Your method is OK but the details leave a bit to be desired.

    5/3 = 1.67 (correct to two decimal places) not 1.68.

    Also, I don't see the point in rounding z to two decimal places and then giving a probability to four decimal places.

    Either use a more accurate value of z or round the probability to less than four decimal places. (Personally I'd do the former).
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