Aaron buys a bag of cookies that contains 8 chocolate chip cookies, 6 peanut butter cookies,7 sugar

Discussion in 'Calculator Requests' started by math_celebrity, May 20, 2020.

  1. math_celebrity

    math_celebrity Administrator Staff Member

    Aaron buys a bag of cookies that contains 8 chocolate chip cookies, 6 peanut butter cookies,7 sugar cookies and 6 oatmeal raisin cookies. What it’s the probability that Aaron randomly selects a peanut butter cookie from the bag, eats it,, then randomly selects another peanut butter cookie?

    First draw out of the bag is a peanut butter cookie:
    P(PB) = Total Peanut Butter Cookies / Total Cookies
    P(PB) = 6/27

    Second draw out of the bag is a peanut butter cookie, but we have one less since Aaron ate one:
    P(PB) = Total Peanut Butter Cookies - 1 / Total Cookies - 1
    P(PB) = (6 - 1)/(27 - 1)
    P(PB) = 5/26

    Now, since each event is independent, we multiply them to see the probability of choosing a peanut butter cookie, eating it, then reaching in and choosing another peanut butter cookie:
    P(PB, PB) = 6/27 * 5/26
    P(PB, PB) = 5/117
     

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