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Math Help - Basic stats/probability problems help please -___-

  1. #1
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    Basic stats/probability problems help please -___-

    I have a couple questions regarding, well, a couple questions.

    1.) A jar contains four coins: a nickel, a dime, a quarter, and a half-dollar. Three coins are randomly selected from the jar.
    (a) List the simple events in S. (Use N for nickel, D for dime, Q for quarter, and H for half-dollar.)
    (b) What is the probability that the selection will contain the half-dollar? (Enter an exact number as an integer, fraction, or decimal.)
    (c) What is the probability that the total amount drawn will equal 55 or more? (Enter an exact number as an integer, fraction, or decimal.)
    okay, forgive me if this is a dumb question, but with a question like this, does order matter? For instance, would NDQ be different than QDN?

    also,

    2.)
    A student prepares for an exam by studying a list of 10 problems. She can solve 3 of them. For the exam, the instructor selects 2 questions at random from the list of 10. What is the probability that the student can solve all 2 problems on the exam? (Enter an exact number as an integer, fraction, or decimal.)

    My answer is 0.0333. With my teacher, I only get three chances to get the answer correct, so I just wanted to see if this was correct.


    Thank you in advance
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  2. #2
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    Re: Basic stats/probability problems help please -___-

    Hey spark062.

    For number 2, it's best if you draw a tree diagram.

    You will have four leaves corresponding to no matches, 1 match, and 2 matches.

    For the branch with two matches we have the first question with a probability of 3/10 since we start off with 10 questions of which 3 of them are ones we know. The second one however has only 9 choices (since we picked 1) with 2 of them being ones we can solve.

    Both choices are independent which means we can apply P(A and B) = P(A)P(B) with P(A) = 3/10 and P(B) = 2/9. P(A and B) = 3/10*2/9 = 6/90 or given by R,

    > 6/90
    [1] 0.06666667

    How did you come to the answer that you got? (Also can you show us your working for Q1 to get specific answers on those)?
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