Calculating a Weighted Average Grade

Date: 05/05/2000 at 08:34:25
From: Sam
Subject: Figuring Out a Grade

The following grades make up 100%.

   45% = 3 tests (85, 78, 92)
   25% = final (94)
   15% = project (91.9)
   15% = 3 case questions each worth 25 points (25, 25, 23.5)

What is the final grade to this point?

Date: 05/12/2000 at 13:30:06
From: Doctor TWE
Subject: Re: Figuring Out a Grade

Hi Sam - thanks for writing to Dr. Math.

Here's how I'd figure out the final grade. First, I'd convert any 
non-percentile grades to percentages. In your case, that would be the 
case questions. To convert them to percentages, divide the points 
earned by the maximum number of points, then multiply by 100%. The 
third case question would be:

     23.5 / 25 * 100% = 94%

I'll let you do the other two (they're pretty easy).

Next, I'd find the averages for all the items that have more than one 
grade. In your case, this would be the tests and the case questions. 
To find the average, add up the grades and divide by the number of 
grades. For the tests, the average would be:

     (85 + 78 + 92) / 3 = 85

Now you need to find the "weighted average" of each of these items. 
Convert their percentage weight (the 45% for tests, for example) to a 
decimal by dividing by 100 (or simply moving the decimal point two 
places to the left) and removing the percent sign. Then multiply the 
grade for that item by this decimal. For example, for the tests you 
get:

     45% = 0.45

so

     85 * 0.45 = 38.25

Do this for each item and add the results. That's the final grade. (If 
a 90 is the cutoff for an A, I think congratulations are in order.)

I hope this helps. If you have any more questions, write back.

- Doctor TWE, The Math Forum
  http://mathforum.org/dr.math/