I'm confused on this problem and don't think I have it right:
Suppose that weekly use of gasoline for motor vehicle travel by adults in North Amercia has approximately a normal distribution with a mean of 20 gallons and a standard deviation of 6 gallons. Many peiole who worry abou global warming believe that Americans should pay more attention to energy conservation. Assuming that the standard deviation and the normal shape are unchanged, to what level must the mean reduce so that 20 gallons per week is the third quartile rather then the mean?
Assuming that there talking about the general standard deviations of the bellcurve, would it reduce by 1 S.D? So that you'd get 20-1(6) = 14 gallons? So then it would reduce by 6 to get to the third quartile? If that's wrong, can someone steer me towards the right direction?
Another one I'm a little bit stuck on is this one:
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.
Suppose that weekly use of gasoline for motor vehicle travel by adults in North Amercia has approximately a normal distribution with a mean of 20 gallons and a standard deviation of 6 gallons. Many peiole who worry abou global warming believe that Americans should pay more attention to energy conservation. Assuming that the standard deviation and the normal shape are unchanged, to what level must the mean reduce so that 20 gallons per week is the third quartile rather then the mean?
Assuming that there talking about the general standard deviations of the bellcurve, would it reduce by 1 S.D? So that you'd get 20-1(6) = 14 gallons? So then it would reduce by 6 to get to the third quartile? If that's wrong, can someone steer me towards the right direction?
Another one I'm a little bit stuck on is this one:
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.
