Weighted average

The quantity

$$ \overline{x}\; = \ \frac{\sum _ {i = 1 } ^ {n} p _ {i} x _ {i} }{\sum _ {i = 1 } ^ {n} p _ {i} } , $$

where $ x _ {1} \dots x _ {n} $ are $ n $ quantities taken with respective weights $ p _ {1} \dots p _ {n} $.