I'm wondering if there is something wrong with how an Average column is calculated in Blackboard Learn.

From Blackboards website they give the following example

Example:

Three values: 8/10, 3/5, 2/2

Percentage equivalents: 80.0000%, 60.0000%, 100.0000%

Total of the values: 240.0000

Number of items: 3

Total value divided by number of columns: 240.0000/3 = 80.00%

When I use the values in Blackboard I actually get the following results.

Anyone know why it would come up with 79.99989% instead of 80%

Also when looking at the AVG points for the assignment it shows 4.53 points but if I multiply that by 3. I get 13.59 instead of 13.

Is there something wrong with the formula in Blackboard or am I just not grasping how the Average should be calculated.

Thanks, Steve

It is fun to try to figure out what other people are thinking!

This is a mess of averages with some round off error thrown in for good measure......

1. Find the average of the percents. In your case, (0.80+0.60+1.00)/3 = 0.80

2. Based on the average percent, find the number of points earned on the assignment: 17*0.80 = 13.6

3. Calculate the average number of points over the 3 assignments by dividing the points by the number of assignments 13.6/3 = 4.5333333....

(So that is where the 4.53 points comes from).

4. Calculate the average number of points on the assignments: 17/3 = 5.66666666....

5. Calculate the average of the assignments: Since the percent in your example is rounded to 5 decimal places, I just took a guess and rounded the answers in steps 2. and 3. to 5 decimal places before dividing. You get 4.53333/5.66667 which is approximately 0.7999989412. If you convert that to a percent and round to 5 decimal places you get 79.99989%. Five decimal places may not be the magic number for rounding but I think there is definitely some rounding going on.

This may not be the order that the calculations occur programmatically in the background but it works for the test cases I tried. To answer your question if something is wrong......I don't think so. If you are just interested in the percentage it seems like a long way around to find what we knew in step 1. However if you are interested in points and still equalizing the weight of the assignments then there has to be some calculation like this to be done.