Yes,
Mean is given by, E(X) sum of samples / no. of samples.
Variance is Var.(X) = E(X^2) - [E(X)]^2.
It is the 1st term which makes the variation of variance independent of mean.
In other words, Variance gives a measure of how far the samples are spread out.
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yes
Because it is in same units as the original data. For example, if you have a sample of lengths, all in centimetres, the sample variance will be in units of centrimetres2 which might be more difficult to interpret but the sample standard deviation with be in units of centimetres, which would be relatively easy to intepret with reference to the data.
Yes.
They should be smaller for the sample size 80.
Adverse variances means unfavourable variance which is actual expenses are more than budgted variance.