Guity
A weighted average is where you have 2 variables and the average variable of interest is not simply the sum of one variable divided by the total, but is a weighted average based on both variables
eg:
I have 2 gold bars that have a content of 10g/t gold and 20g/t gold
The arithmetic average of the content of gold will be 15g/t gold: (10+20)/2
But if I now tell you that the 10g/t bar weighs 1kg and the 20g/t bar weighs 5 kg
the weighted average is:
[(10x1)+(20*5)]/6
= 18.33 g/t gold
A good way to do weigted averages is to use SumProduct, as it multiples the 2 variables and adds the result
You then need to divide by the sum of the other variable
eg:Average Gold Content =Sumproduct(Weight Range, Gold Range) / Sum(Weight Range)
It is worth noting that a variable may have more than 1 weighting variable and in this case you need to multiply all variables togther and dividen by the sum of the other vaiables multiplied together exluding the variable you are measuring
eg:
=Average Content =Sumproduct(Variable 1 Range, Variable 2 Range, Gold Range) / Sumproduct(Variable 1 Range, Variable 2 Range)