computing average in nested loops

[cap510]

I can't seem get class weighted average to compute correctly. I ran program with placement under the two different loops, but each time it gave me an incorrect number.

students = ['Tony', 'Steve']
category = [ 'Assignment', 'Quizzes', 'Projects', 'Essays', 'Exams']
weighted = [.1, .1, .3, .25, .25]
cwave = []
total2 = 0
total3 = 0
for i in students:
    print(i)
    total = 0

    for num in weighted:
        score = float(input('Enter scores: ')) * num
        total += score
        total /= sum(weighted)
        total2 += total
        total2 /= len(students)
        if total >= 89:
            letter = ('A')
        elif total >= 79:
            letter =('B')
        elif total >= 69:
            letter =('C')
        elif total >= 59:
            letter =('D')
        else:
            letter =('F')
    print('Wieghted average = ' + str(total))
    print('Wieghted Letter Grade: ' + (letter))
print('Class Weighted Average: ' + str(total2))

This is what returns - It should compute to 84.225 -no error message:

Error:
/Users/cesarperez/PycharmProjects/Assign7/venv/bin/python /Users/c/Downloads/#4.py
Tony
Enter scores: 95
Enter scores: 95
Enter scores: 80
Enter scores: 85
Enter scores: 82
Wieghted average = 84.75
Wieghted Letter Grade: B
Steve
Enter scores: 90
Enter scores: 87
Enter scores: 80
Enter scores: 78
Enter scores: 90
Wieghted average = 83.7
Wieghted Letter Grade: B
Class Weighted Average: 65.79052734375

Process finished with exit code 0

[micseydel]

I'll start with one hint: what is the value of sum(weighted)?

[cap510]

sum(weighted) = 1. The value of

    for num in weighted:
        score = float(input('Enter scores: ')) * num
        total += score
        total /= sum(weighted)
        total2 += total
        total2 /= len(students)

is what I am trying to use. Since sum(weighted) = 1, does it affect the value of total?

[micseydel]

Since sum(weighted) = 1, does it affect the value of total?

Well, if you were adding it to a number, it would affect it (a little bit). But dividing by 1 has no impact, so the line could be omitted. If that were true, then your algorithm would be able to calculate a weighted average without knowing the weights, but that's clearly absurd.

What I was hoping you'd do was realize that your algorithm is wrong, and google weighted average[ :).

In calculating a weighted average, each number in the data set is multiplied by a predetermined weight before the final calculation is made.

If you're still not sure, I recommend working it out on paper first. Also, I know some people learn well from Youtube (I'm not one of them) so that may be another way to try to learn about weighted averages.

[buran]

@micseydel - they multiple by weight on the same line (12 or 2 in the different snippets they post) on which they take the input (num is actually respective weight). But of course you are right - they have weights in range (0-1) and sum of weights is 1, so there is no need to divide by 1. I was thinking to comment on this in the other thread but it slipped from my mind when posting an answer.

EDIT: I see your point now

[deanhystad]

Though you get the correct answer for a student's weighed average this is only because the sum of the weights is 1. Try changing your weights to [10, 10, 30, 25, 25]. This should compute the same weighted average as [0.1, 0.1, 0.3, 0.25, 0.25] but it does not when run in your program.

Fixing the above problem should point out the error you are making calculating the classroom average.