Thread: Help deriving an equation.

I believe that the following two equations are equivalent, but I am unable to algebraically derive one from the other. For computing a running average, I believe the following formula is correct where n = number of values in oldMean:

.

Similarly, I found this equation which I think does the same thing:

.

Are these equations in fact equivalent? They both seem to work when calculating a running average. If they are equivalent, how do I derive one from the other?

Thank you. This seems like an easy problem, but I've managed to confuse myself.

Let's denote oldMean by m, newMean by m' and newVal by v. Then