5 text cm 52 52 2 5 text cm2 25 text cm2 10 textOr 10 text m 33 1000 text m3 3 3 1000 text m3 9. If we imagine each measurement to be equal to the true value plus some random error then the sum of Nmeasurements will be equal to Ntimes the true value plus the sum of all the random errors. When you calculate the mean of a set of measurements you sum the measurements and then divide by N the number of measurements in the set.
This is easy to do in Excel with the AVERAGE function.
However the uncertainty of the average value is the standard deviation of the mean which is always less than the standard deviation. However it is often unclear how the standard uncertainty associated with averaged results should be calculated from an observed standard deviation. Now to find the uncertainty in the average without going into a bunch of details just add the uncertainties of each in quadrature and divide by the square of the number of terms-- so total. Note that the adjustment coefficient Nj-1Nj is needed only if you computed Vj using Nj-1 as the number of statistical.