[Statistics] measuring values against known value

[Chickenpoxpie]

Homework Statement

You use a standard gram weight of known weight (x) to check the accuracy of a balance. For one balance, this standard is weighed 3 times yielding the following values; a, b, and c. Calculate the 95% confidence limit for the mean

Homework Equations

general statistics and mean equations
ts/n^1/2

The Attempt at a Solution

I am confused how to do this problem because of the known value. At first I did the problem ignoring the known value and going through all the motions (figuring the mean, standard dev, and then plugging into ts/n^1/2 for 2 degrees of freedom) but how do things change because of the known weight and "testing for the accuracy of the balance"?

 

[Chickenpoxpie]

Nevermind y'all, was a silly mistake. I can easily do a one sample t test