http://www.mathwords.com/w/weighted_average.htm
At the above link gives an example of a weighted average. It uses the

following example:

Grades are often computed using a weighted average. Suppose that

homework counts 10%, quizzes 20%, and tests 70%.

If Pat has a homework grade of 92, a quiz grade of 68, and a test grade

of 81, then

Pat's overall grade = (0.10)(92) + (0.20)(68) + (0.70)(81)

= 79.5

I have created a weighted average similar to the above model for quality

assurance. And it works fine.

Now I've been asked to provide a weighted average for the price of the

project. How does one "blend" or "merge" two weighted averages

together? Does one simply add the weighted averages together and divide

by the number of averages...or does one assign weights to each weighted

average to determine the weighted average of the weighted averages?

(That's a tongue twister).

Anyway, if you have any input on weighted averages I'd appreciate your

insite.