Overview
This is a more technical guide on setting up a mathematical "weighted average" using the Gradebook's "add calculation" tool. This is not as simple as setting up the overall grade (See guide here for Overall Grade), and is more directed at experienced Gradebook users.
Details for the tool, "Calculate Grades"
Refer to Blackboard documentation here: https://help.blackboard.com/Learn/Instructor/Ultra/Grade/Grading_Tasks/Calculate_Grades for a summary on the technical pieces of this tool.
Understanding the Weighted Average
When performing weighted calculations, it is crucial to include the 'possible' points in the formula. Failure to do so will default to a possible point value of 100. Therefore, the correct formula should be as follows:
(Points obtained / Points possible) * Percentage
The calculation above is a smaller piece in a larger calculation.
Data
To illustrate this, let's review the scenario of Sam Student, who received the following grades on their assignments:
| Name | Weight (% of grade) | Points Possible | Grades/Points Obtained (Sam Student) |
| Assignment 1 | 10% | 20 | 19 |
| Assignment 2 | 10% | 20 | 17 |
| Assignment 3 | 10% | 50 | 48 |
| Assignment 4 | 15% | 20 | 15.5 |
| Assignment 5 | 25% | 50 | 34.5 |
| Assignment 6 | 25% | 50 | 45 |
| Assignment 7 | 5% | 1 | 0.5 |
| Total Weight | 100% |
Understanding the Weighted Average Calculation
Below is an expanded line-by-line example of a weighted average calculated in excel. Using the initial formula above to create the outcome, then summing the outcome to create the full weighted average. This can be done in excel using the manual calculation below, or by using the formula SUMPRODUCT().
| Name | Weight (Normalized to out of 1) | Points Possible | Grades (Sam Student) | Formula | Outcome |
| Assignment 1 | 0.1 | 20 | 19 | (19/20)*0.1 | 0.095 |
| Assignment 2 | 0.1 | 20 | 17 | (17/20)*0.1 | 0.085 |
| Assignment 3 | 0.1 | 50 | 48 | (48/50)*0.1 | 0.096 |
| Assignment 4 | 0.15 | 20 | 15.5 | (15.5/20)*0.15 | 0.11625 |
| Assignment 5 | 0.25 | 50 | 34.5 | (34.5/50)*0.25 | 0.1725 |
| Assignment 6 | 0.25 | 50 | 45 | (45/50)*0.25 | 0.225 |
| Assignment 7 | 0.05 | 1 | 0.5 | (0.5/1)*0.05 | 0.025 |
| TOTAL | 0.81475 | ||||
| TOTAL (Percentage) | 81.475% |
While it is useful to create this in excel, we want to create this in Blackboard as well...read on traveler.
Create the Weighted Average
Adding a Calculation
Typing in the Weighted Average Calculation
Fair warning, this next part is extremely tedious. The entire calculation must be typed in, including all mathematical operators, parentheses, variables, and weights. This can only be done with individual columns. It is not recommended to use categories to represent a group of assignments.
The below is an example of a fully typed in weighted average.
For the assignment name, use Variable. This will allow you to select a specific gradebook assignment. Mathematical operators can be used by clicking them. To enter the points possible and the weights, use the operator value.
Once all of the calculations are typed in, you can click save. The weighted average will now calculate for each student.
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