# Confidence Interval Help!

• Apr 24th 2008, 09:47 AM
tysupplyguy
Confidence Interval Help!
A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were
3.087
3.131
3.241
3.241
3.270
3.353
3.400
3.411
3.437
3.477
(a) Construct a 90 percent confidence interval for the true mean weight.
(b) What sample size would be necessary to estimate the true weight with an error of ± 0.03 grams with 90 percent confidence?

This is what I got so far? Im lost!
3.3115 ± 1.645 (0.131988888)/√10 =
• Apr 24th 2008, 12:42 PM
TKHunny
You are not lost. You are very close.

However, I'm a little curious how you managed to get the Standard Deviation right but not the Mean? Try that Mean again.

For the second part, contemplate $1.645*\frac{0.131988888}{\sqrt{n}} < 0.03$

HOWEVER, and this is a very large HOWEVER, it had better be a VERY LARGE bag of Tootsie Rolls!

You have a choice...

Tell me why it needs to be a very large bag, or
Tell me how you plan to implement the Finite Population Correction Factor.
• Apr 28th 2008, 05:04 AM
tysupplyguy
Hey ok The mean is 3.305. I dont quit understand this method. The teacher I have hasnt really shown us much on this. I somewhat know how to use this formula but what it actually does I dont know.
• Apr 28th 2008, 05:17 AM
mr fantastic
Quote:

Originally Posted by tysupplyguy
A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were
3.087
3.131
3.241
3.241
3.270
3.353
3.400
3.411
3.437
3.477
(a) Construct a 90 percent confidence interval for the true mean weight.
(b) What sample size would be necessary to estimate the true weight with an error of ± 0.03 grams with 90 percent confidence?

This is what I got so far? Im lost!
3.3115 ± 1.645 (0.131988888)/√10 =