## Jovanmommy_13 Group Title 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

1. FeoNeo33 Group Title

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

2. FeoNeo33 Group Title

By the way, I made up that way to get the answer, not a real technique.

3. amistre64 Group Title

im thinking it sounds like a binomial probability setup

4. Jovanmommy_13 Group Title

that what these are

5. amistre64 Group Title

125 C 70 times success^(70) times failure^(125-70) 125 C 70 (1/2)^(70) (1/2)^(125-70) soo:$\sum_{k=70}^{125}\binom{125}{k}.5^{k}.5^{125-k}$

6. amistre64 Group Title

or we can try a normal approximation :)

7. amistre64 Group Title

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)

8. amistre64 Group Title

do you have to do this all by hand or do you have a ti83?

9. amistre64 Group Title

$z=\frac{x-mean}{sd}$ $z=\frac{70-62.5}{\sqrt{31.25}}=1.34$ looking on a ztable; that corresponds to about 100% - 91%

10. amistre64 Group Title

so yeah, it aint gonna be B, but it does look like it will be close to 10%