# Excel data analysis

Not sure where to post this question, but here goes

In excel I have calculated the average annual rain for the period 1990-2012 to be 50.2mm . How do you estimate the probability that this measured average (1990-2012) is consistent with the long term mean annual rain for the period 1948-2012 (assuming a gaussian distribution) which I calculated to be 51.6mm?

Is there some sort of function or is this simpler than I'm imagining...

any help much appreciated

thanks

Simon Bridge