Exponentially weighted moving average result in a single function\cell

Is it possible to calculate an exponentially weighted moving average across a set of data without having to calculate each period separately?

This is similar to =SUMPRODUCT(array1,array2)/sum(array1) however in my case, I need to take 80% of all of the prior periods result and adding 20% of the current period. There could be 200+ prior periods so a simple weighted average will not work.

I have tried MMULT, VPV and a number of loan\investment functions already. I may just not know what to search for.

I have added a worksheet demonstrating the problem.