1. ## Re: Finding Standard Deviation

Still smells like a hypothesis test to me.

And I take back my comment of:

Originally Posted by trinker
Null (H0's) hypotheses are not written in terms of alpha.
I did not read carefully this was P not a pvalue.

2. ## Re: Finding Standard Deviation

PhatKroger10 please listen to BMG and Dason they're both more knowledgeable than I am. I'd wait to see what they have to say.

3. ## Re: Finding Standard Deviation

If it is of any help, here is the hint given to me following my first failed attempt.

"The number of calculators returned for refund or replacement is a random variable with a binomial distribution. Find mean and standard deviation."

4. ## Re: Finding Standard Deviation

It is a binomial probability calculation like we mentioned before. I think why they want you to get the mean and standard deviation is that your calculator probably can't handle the numbers required to do an exact binomial calculations so you'll probably need to do a normal approximation.

5. ## Re: Finding Standard Deviation

Originally Posted by Dason
It is a binomial probability calculation like we mentioned before. I think why they want you to get the mean and standard deviation is that your calculator probably can't handle the numbers required to do an exact binomial calculations so you'll probably need to do a normal approximation.
I don't believe it mentions mean anywhere in the problem. I will look up how to do a binomial calculation on my TI-83+ and inform you of the results.

6. ## Re: Finding Standard Deviation

The 83 might be able to do it directly for you. I don't remember what probability capabilities it had.

7. ## Re: Finding Standard Deviation

I am kind of confused, is the PHat .05 or .058. I understand the QHat is 1-PHat, but am having difficulties on differentiating which is the PHat.

8. ## Re: Finding Standard Deviation

http://users.rowan.edu/~schultzl/ti/binomial.pdf

Via the site above my calculator equation shows:
binompdf(500,.05, 29)=.0552
n=500, p=.05, x=29, p=.0552

I entered this online in my homework and it said that it was incorrect. Is there something I am doing wrong here?

9. ## Re: Finding Standard Deviation

Ok I double check your work in R once more:

> dbinom(29,500,0.05)
[1] 0.05520704

Maybe that online question really want you to use the normal approximation. The approximation is not very good as the binomial distribution is (highly) skewed and it is near the tail area.

Caution: Here is the computation in R with continuity correction. Only check it when you have try the hints given by Dason - computing the mean and variance, and understanding the usage of Central Limit Theorem.

Spoiler: