Author's Thought

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Sunday, February 26, 2012


So, it's report card time soon. And I'm sure that I'm not the only one to calculate my overall average as soon as I get all my marks! But does everyone do it the right way?

Okay, let's make a situation with my friend Bob:

Bob's school has a 6-day cycle system.
Bob's got 5 different courses.
Here are Bob's courses and marks:

  • Math: 81%
  • French: 68%
  • English: 87%
  • Science: 73%
  • P.E.: 95%

Bob has Math and English 6 times a cycle (100% of the cycle);
he has French and Science 4 times a cycle (let's say 67% of the cycle) and
he has Physical Education once a cycle (let's say 17% of the cycle).

Bob here wants to know his overall average and doesn't have the patience to wait for the Honor Rolls, if he's even on it (we'll solve this mystery, Scooby!).

So this is da' formula you's gonna use Bobby:

where "T" is the total percentage (overall; in %), "P" is the percentage for a class and "C" is the percentage of the number of classes you have for that course for a cycle.

Let's fill in the blankies, shall we?

T = (81•100)+(68•67)+(87•100)+(73•67)+(95•17)/(100+67+100+67+17)
T = (8100)+(4556)+(8700)+(4891)+(1615)/(351)
T = (27 862)/(351)
T = 79.37%

Bob is still not satisfied! He wants to know why he has such a low mark in French. Luckily this also works for competencies―and much more!

So, let's see. There are two competencies: Talking (worth 45%) and writing/comprehending (worth the other 55%). For these competencies, he got 83% and 56%. That 83% is why he's so astonished about his mark! Let's see here:

T = (P1•C1)+(P2•C2)/(C1+C2)
T = (83•45)+(56•55)/(45+55)
T = (3735)+(3080)/(100)
T = (6815)/100
T = 68.15%

Now Bob has nothing to whine about and is satisfied! :)

Are you satisfied?

1 comment:

  1. Excellent process, perfect formula, great examples. I always like to look at the result of a weighted average and ask myself "Which nbr should the result be closest to?" and it's usually the one with the heaviest weight. SO his 79% is good because he has some 80's that are heavy! The only thing I would change would be to use codecogs for your fractions!