Uncertainty of Mean Values

[Squidiemeister]

I am trying to find the uncertainty of the mean of 3 values.
These values were calculated from experiments to calculate the enthalpy change of various alcohols.
These values are independent values.

−283 ± 11, −175 ± 9, −282 ± 11

How would I calculate the uncertainty of these values?
Thank you.

 

[Simon Bridge]

Welcome to PF;
You use the rules for propagation of uncertainties...
Have you seen: https://www.physicsforums.com/threads/uncertainty-of-an-average.612633/

 

[Vanadium 50]

If those numbers are supposed to be measurements of the same thing, I wouldn't average them. Do you know why?