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Jovanmommy_13

What is the probability that out of 125 babies born, at least 70 will be girls? Assume that boys and girls are equally probable, and round your answer to the nearest tenth of a percent. A.99.0% B.70.4% C.10.5% D.51.2%

  • one year ago
  • one year ago

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  1. FeoNeo33
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    10 20 30 40 50 60 70 / 80 90 100 110 120 ...125 70 / 50... Which I pick... B.

    • one year ago
  2. FeoNeo33
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    By the way, I made up that way to get the answer, not a real technique.

    • one year ago
  3. amistre64
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    im thinking it sounds like a binomial probability setup

    • one year ago
  4. Jovanmommy_13
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    that what these are

    • one year ago
  5. amistre64
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    125 C 70 times success^(70) times failure^(125-70) 125 C 70 (1/2)^(70) (1/2)^(125-70) soo:\[\sum_{k=70}^{125}\binom{125}{k}.5^{k}.5^{125-k}\]

    • one year ago
  6. amistre64
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    or we can try a normal approximation :)

    • one year ago
  7. amistre64
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    mean = np = 125(.5) = 62.5 so we would expect 62.5 of the population to be girls sd = sqrt(npq) = sqrt(62.5*.5) = sqrt(31.25)

    • one year ago
  8. amistre64
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    do you have to do this all by hand or do you have a ti83?

    • one year ago
  9. amistre64
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    \[z=\frac{x-mean}{sd}\] \[z=\frac{70-62.5}{\sqrt{31.25}}=1.34\] looking on a ztable; that corresponds to about 100% - 91%

    • one year ago
  10. amistre64
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    so yeah, it aint gonna be B, but it does look like it will be close to 10%

    • one year ago
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