The phrase "average number" refers to finding a typical or representative value in a group of numbers. It is calculated by adding up all the numbers in a set, then dividing the total by the quantity of numbers. Full definition
What is your past average number of days on the market? (rismedia.com)
Despite this drop in average number of games being sold for each system, the sales results for the latest consoles remain very strong eight months after launch. (npd.com)
Fuel economy comes in at 16 mpg city and 23 mpg highway, pretty average numbers for this size of engine. (cnet.com)