In the Quick measures window under Calculation select Average per category. However when a cell contains a blank the row is not counted. The formula for finding the weighted average is the sum of all the variables multiplied by its weight then divided by the sum of the weights.
The weighted average is calculated as the sum of all of the values multiplied by their weights divided by the sum of all of the weights.
Monthly Weight which is Monthly Sales Annual Sales. AVERAGE DAX Function in detail. Lets Look at an Example. Ive seen this requested many times on the Enterprise DNA Support Forum and elsewhere.