Weighted Average question

[Salad]

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.

[CDMAPoster]

On Sep 5, 5:28 pm, Salad <[e-mail]:

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.

The way weighted averages weigh in is to the way the weight weighs out
the best :-). (I wanted to use the word 'wait' also but I wanted the
sentence to make sense.) The important thing is that the method makes
sense in the given context. I can imagine situations where either an
average of averages or a weighted average of averages would be
appropriate. If the weights are independent, such as the calculation
of an overall grade given overall grades for different classes, you
still might need to use the number of credits in a weighted average to
get an overall grade. If the weighted averages are not independent
(i.e., they both contain some of the same factors), then it may be
necessary to look into it further to keep a factor from contributing
more than it should.

James A. Fortune
CD********@FortuneJames.com

[Fred]

On Thu, 06 Sep 2007 13:11:13 -0700, CD********@FortuneJames.com wrote:

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

Please explain this part.

Thanks.

[Larry Linson]

You need to ask the person who asked you for the "weighted average for the
price of the project" to define what they want. They will need to tell you
what 'weight' they assign for each item.

Larry Linson
Microsoft Access MVP