# Thread: Confidence interval for variance-need ur help-exam after 2 days

1. ## Confidence interval for variance-need ur help-exam after 2 days

Confidence interval for variance

In 16 test runs the gasoline consumption of an experimental engine had a slandered deviation of 2.2 gallons. Find 99% confidence intervals for variance , which measures the true variability of the gasoline consumption of the engine.

Solve it using this rule:

http://sixsigmatutorial.com/Six-Sigma/Six-Sigma-t-Confidence-Interval-Variance.aspx

N=16
S^2=(2.2)^2

I don't know how to calculate x^2 alpha/2,n-1

2.21< < 15.78

2. Originally Posted by neverlosehope
Confidence interval for variance

In 16 test runs the gasoline consumption of an experimental engine had a slandered deviation of 2.2 gallons. Find 99% confidence intervals for variance , which measures the true variability of the gasoline consumption of the engine.

Solve it using this rule:

http://sixsigmatutorial.com/Six-Sigma/Six-Sigma-t-Confidence-Interval-Variance.aspx

N=16
S^2=(2.2)^2

I don't know how to calculate x^2 alpha/2,n-1

2.21< < 15.78
Using an on-line calculator: Chi Square Calculator

I get $\displaystyle \chi^2_{df=15, \, 0.005} = 32.8$. (Total time: 10 seconds using google).

Critical values are typically got from a table, especially in examinations. In an examination, you obviously won't be asked to find something that isn't on the table so you have nothing to worry about.

3. thanks but can u tell me how can i get the number from the chi square table

4. Originally Posted by neverlosehope
thanks but can u tell me how can i get the number from the chi square table
Show us the table you're using.

5. I have this book:
statistical techniques in business & economics with global data sets

linda.marchal.wathen 13E

page 787
B.3 critical values of chi-square

i don't know if u have that book

6. Originally Posted by neverlosehope
I have this book:
statistical techniques in business & economics with global data sets

linda.marchal.wathen 13E

page 787
B.3 critical values of chi-square

i don't know if u have that book
No I don't. I suggest you discuss the matter with your instructor (getting the critical value from the table, not my not having the book).

As I said previously, if the critical value is not included in the tables you use for your examination, you will not be required to use it in the examination unless it was given.

7. Thank you so much for your effort