Stats problem

[Violagirl]

There is a magazine for small children called "Wild Animal Baby" which is published by the National Wildlife Federation. Each issue they write a feature story about a different baby animal with an alliterative first name, such as Wanda the Walrus or Cody the Coyote. There are 10 issues published each year. If the magazine chose the gender of the baby animal randonly, the probablility that the feature story is about a girl would be 50%.

A) What is the probablility that, in a year, the first three issues feature a girl baby animal, the next 4 feature a baby boy animal, and the last three feature a girl baby animal?

To set this up, would it be 4(.50)+3(50)+4(.50) to get the probability?

B)What is the probability that, during a year, only three issues have the feature story about a girl baby animal?

Wouldn't it be 15% if you take 3/10 which is 30% mulitplied by .50?

C) What is the average number of times you'd expect to have the feature story be about a girl baby animal in a year? What is the standard deviation?

I'm not sure how to determine this as there isn't a clear set of numbers given to sum together but I believe you'd have to divide by 10. And for the S.D., I'm not sure by what they want for it...

D) How many issues would you need to sample (what size n do you need) before you could use the normal approximation for the binomial? Round your anwer to the nearest whole number

???

 

[tkhunny]

A: 4(.50)+3(50)+4(.50)

Wow! Please be more careful and actually think about what you are doing, rather than just writing stuff down. Really, this is a very poor effort.

1) 4 + 3 + 4 = 11 -- There's only 10. Whoops. Even if we fix that, and the typo:
2) 3(.50)+3(.50)+4(.50) = 10*0.50 = 5. That is a VERY LARGE probability, particularly considering that 1 (one) is the maximum permissible.

Are the events independent? Is that sequence any more probable than any other sequence?