got a stats question...last time nyc helped me

[nycgirl]

hey NYC, if your not comfortable msgn me thats fine.

the last prob im working with is this...


Does the sample evidence indicate that the average time an employee stays with a company in their current positions is less than 3 years? A random sample of 50 employees yielded a mean of 2.79 years and s = .76. Use a = .01

Good lord. No need to make me look weird. I just sent you a PM.

I will give these a try. But, I think you are going to have to guess. This was never my strong point in stats.

 

[bran987]

it tells you it's a normal distribution so use the Z-table. Look up the Z-score for a 95% confidence interval (i.e. 2.5% on each side, so find the score that gives you 2.5% on each side, I think it's 1.96?)

Instead of converting "X" to a standard normal distribution, reverse the formula and convert the Z-score backwards to give "X" and use the standard deviation in the formula given by the square root of the variance (square root of 1900 = 43.59). So the only variable left to solve for in the equation will be the mean.

X = u + (std. dev. * z-score)

It's the inverse of the standardization rule in other words.

I think.

 

[bran987]

oh wait no hold on

 

[doubles1]

bran,

thanks a lot...i am startin to struggle now been at this for 3+ hrs now.

 

[bran987]

to get the sample size you take n = p (1 - p) * (z alpha/2 / MOE) so we need to solve for N here...

So I think here that would be

 

[bran987]

bran,

thanks a lot...i am startin to struggle now been at this for 3+ hrs now.

what I posted up there in that first post is wrong lemme work on this for another minute haven't done it in awhile. So it's asking for "within 20" so that's the margin of error? it doesn't ask for a certain percentage margin of error right?

 

[doubles1]

hey bran it asks for

What sample size is needed to estimate with 95 percent confidence the mean intake of calcium within 20 units of the true mean if the intake is normal with a variance of 1900 units?



The last question on the test is this..and i am strugglin like a champ...

A random sample of 100 European professional soccer players has an average age of 27 years. The sample standard deviation is 4 years. We would like to decide if there is enough evidence to establish that the average age of European soccer players is more than 26 years.

Answer A B & C Below:

A. Write the null hypothesis.

B. Write the alternative hypothesis.

C. What is the rejection point (given in terms of the value of the test statistic) at a = .05?

 

[bran987]

nycgirl last time you helped me however i have another problem that I am needing help with...

i will gladly give sum karma

here is the problem:

What sample size is needed to estimate with 95 percent confidence the mean intake of calcium within 20 units of the true mean if the intake is normal with a variance of 1900 units.

thanks for any assistance.

-mark

I think the answer to this one is n = ((1.96 * sqrt(1900))/20) ^ 2 = 18.25

n = 18.25

 

[seizer]

sucka, you gotta take stats!


and here I am with 6 hours of bio a head of me....

 

[bran987]

hey bran it asks for

What sample size is needed to estimate with 95 percent confidence the mean intake of calcium within 20 units of the true mean if the intake is normal with a variance of 1900 units?



The last question on the test is this..and i am strugglin like a champ...

A random sample of 100 European professional soccer players has an average age of 27 years. The sample standard deviation is 4 years. We would like to decide if there is enough evidence to establish that the average age of European soccer players is more than 26 years.

Answer A B & C Below:

A. Write the null hypothesis.

B. Write the alternative hypothesis.

C. What is the rejection point (given in terms of the value of the test statistic) at a = .05?

A) Null Hypothesis: u = 26 (or u > 26)
B) Alternate Hypthothesis: u does not = 26


now for C, hold on