What is the summation of one set real numbers divided by the cardinality of another set called? $$A \subset\mathbb R$$ $$\frac{\sum A}{|B|}$$
I will try and be specific to my problem because I lack the skill to properly define the relationship between the A and B sets.
A is a set that contains the dollar figure of invoices to our marketing department for their advertising.
B is a set that is the sales leads/interactions that are a result of the marketing purchases.
The aim is to tie an average dollar figure to each sales lead based on the total marketing spend and the volume of leads produced.
As an example, A may contain 2 elements with attributed dollar values of \$100 and \$40, at that time there are 70 elements within the B set; I expect the result to be $2.
It's a ratio you dope!
See the definition here.