SparkimusPrime
Mar21-04, 02:15 PM
Edit:
Moved from statistics -
http://www.physicsforums.com/showthread.php?s=&postid=164120#post164120
I'm doing some homework over the break (!) so I don't have access to my usual lines of help. I've hit a wall:
A cereal manufacturer packages cereal in boxes that have 12-ounce label weight. Suppose that the actual distribution of weights is N(12.2, .04).
a) What percentage of the boxes have cereal weighing under 12 ounces?
b) if x-bar is the mean weight of the cereals in n = 4 boxes
selected at random, compute P(x-bar < 12).
I don't really know how to solve a problem like this, from the replies to the previous thread I know I have no idea of the concepts being discussed here.
Also:
What are the mean and variance of U = sqrt(18) * (w - 2/3)?
0 < w < 1
I get the mean correctly, but the standard deviation does not come out correctly, it integrates to sqrt(2) / 12. Its supposed to be a normal distribution, with mean of 0 and standard deviation of 1, but damned if I know how to integrate the standard deviation correctly:
(this is correct, the notation is standard for the TI-89)
mu = mean = integral( w * sqrt(18) * (w-(2/3)),w,0,1 ) = 0
var = integral(w^2 * sqrt(18) * (w-(2/3)),w,0,1) - mu^2 = sqrt(2) / 12
(this is incorrect, the root of the answer [the standard deviation] is clearly not 1. I think I may in fact be mixing up my equations.)
Peter
Moved from statistics -
http://www.physicsforums.com/showthread.php?s=&postid=164120#post164120
I'm doing some homework over the break (!) so I don't have access to my usual lines of help. I've hit a wall:
A cereal manufacturer packages cereal in boxes that have 12-ounce label weight. Suppose that the actual distribution of weights is N(12.2, .04).
a) What percentage of the boxes have cereal weighing under 12 ounces?
b) if x-bar is the mean weight of the cereals in n = 4 boxes
selected at random, compute P(x-bar < 12).
I don't really know how to solve a problem like this, from the replies to the previous thread I know I have no idea of the concepts being discussed here.
Also:
What are the mean and variance of U = sqrt(18) * (w - 2/3)?
0 < w < 1
I get the mean correctly, but the standard deviation does not come out correctly, it integrates to sqrt(2) / 12. Its supposed to be a normal distribution, with mean of 0 and standard deviation of 1, but damned if I know how to integrate the standard deviation correctly:
(this is correct, the notation is standard for the TI-89)
mu = mean = integral( w * sqrt(18) * (w-(2/3)),w,0,1 ) = 0
var = integral(w^2 * sqrt(18) * (w-(2/3)),w,0,1) - mu^2 = sqrt(2) / 12
(this is incorrect, the root of the answer [the standard deviation] is clearly not 1. I think I may in fact be mixing up my equations.)
Peter