How is the 'Weighted Average Price' calculated?

Weighted Average Price = (sum of (Price multiplied by NumberOfListings) ) / (sum of NumberOfListings)

Here is a simple example. Let's say there are two buckets:

1) Price = 10, NumberOfListings = 5

2) Price = 20, NumberOfListings = 2

Weighted Average = (10*5 + 20*2) / (5+2) = (50+40)/7 = 12.86