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Binomial Probability

  1. Sep 21, 2011 #1
    Hi, the following is a list of binomial cumulative distribution of the probability that out of 25 investors, the number of investors that would have exchange-traded funds in their portfolios.

    We were asked for the probability that at least 14 investors do not have exchange-traded funds in their portfolios from this table.

    Binomial
    n 25
    p 0.4800

    xi P(X<=xi)
    0 0.0000
    1 0.0000
    2 0.0000
    3 0.0002
    4 0.0009
    5 0.0037
    6 0.0124
    7 0.0342
    8 0.0795
    9 0.1585
    10 0.2751
    11 0.4220
    12 0.5801
    13 0.7260
    14 0.8415
    15 0.9197
    16 0.9648
    17 0.9868
    18 0.9959
    19 0.9989
    20 0.9998
    21 1.0000
    22 1.0000
    23 1.0000
    24 1.0000
    25 1.0000

    Here is what I did: since they ask for at least 14 do not, it means 11 or less do. So the answer is .422---the cumulative of 11 and less that do.

    But when I used the Binomial Cumulative Distribution function on my calculator Binomcdf (25, 0.52, 14), I get 0.725.

    Where did I do wrong?

    Thanks.
     
  2. jcsd
  3. Sep 21, 2011 #2

    chiro

    User Avatar
    Science Advisor

    Hey koudai8 and welcome to the forums.

    Since we are given P(X = x) = probability that x people have exchange traded funds, then what is the probability P(Y = y) where y people do not have exchange traded funds related to P(X = x) (In other words how can we write P(Y = y) in terms P(X = x)?
     
  4. Sep 22, 2011 #3
    Is it not 0.52? (probability)
     
  5. Oct 9, 2011 #4

    Atleast 14 do not means 13 or less do,not 11 or less.The compliment of atleast 14 is atmost 13.
     
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