anonymous
  • anonymous
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%
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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anonymous
  • anonymous
10 20 30 40 50 60 70 / 80 90 100 110 120 ...125 70 / 50... Which I pick... B.
anonymous
  • anonymous
By the way, I made up that way to get the answer, not a real technique.
amistre64
  • amistre64
im thinking it sounds like a binomial probability setup

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anonymous
  • anonymous
that what these are
amistre64
  • amistre64
125 C 70 times success^(70) times failure^(125-70) 125 C 70 (1/2)^(70) (1/2)^(125-70) soo:\[\sum_{k=70}^{125}\binom{125}{k}.5^{k}.5^{125-k}\]
amistre64
  • amistre64
or we can try a normal approximation :)
amistre64
  • amistre64
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)
amistre64
  • amistre64
do you have to do this all by hand or do you have a ti83?
amistre64
  • amistre64
\[z=\frac{x-mean}{sd}\] \[z=\frac{70-62.5}{\sqrt{31.25}}=1.34\] looking on a ztable; that corresponds to about 100% - 91%
amistre64
  • amistre64
so yeah, it aint gonna be B, but it does look like it will be close to 10%

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