# My brain hurts- confidence intervals

#### Glass4

##### New Member
I have probably been looking at this problem for too long- it is just a sample problem, not part of an assignment, but I am so stuck! I seem to be able to fint a t-value, I have my sample mean figured out, but I cannot figure out how to find a standard error or a sample standard deviation. I am sure it is just my brain blanking out, but I cannot proceed until I have figure it out! HELP! Problem:

The following are the results of 10 attempts to measure the concentration of nitrate ions (in micrograms/mL) in a specimen of water.

0.513 0.524 0.529 0.481 0.492 0.499 0.518 0.490 0.494 0.501

a) calculate a 95% confidence interval for the true concentration.

I got sample mean= 0.5041
t= 2.262
and I am trying to fit it into the sample mean +/- margin of error equation

Leslie

#### CBABD

##### New Member
program?

What program are you using to analyze your data?

#### CBABD

##### New Member

You should have a formula in your book for calculating confidence intervals. From what I remember these are the elements you need to calculate a confidence interval:

1) a value (like the mean)
2) the standard error of the measure
3) the desired width of the CI

for 1, you can calculate the mean from the data you have.
for 3, you know what this is too from the text of the problem.

If I remember correctly, you will just have to solve for the standard error using the confidence interval formula.

#### Glass4

##### New Member
Thanks, CBABD.

I was overthinking, and once I stopped, I finally got it worked out!