Percentage Got Me Puzzled! It may seem pretty naive and stupid but this problem got me thinking for a very long time.
Assume I have three subject marks: 70 (first), 80 (second), and (76, 67, 90) for the third subject. Percentage is calculated in the following ways.
Max marks of each subject is 100


*

*thirdR = (76 + 67 + 90) / 300; result = (70 + 80 + thirdR)/300; result = 75.88%

*result = (70 + 80 + 76 + 67 + 90)/ 500; result = 76.6
I know that (2.) is a wrong way of calculating percentage but why is there a difference? It kind of seems legit. Is there any correction factor? Thank you in advance

If you expand your first calculation, you get $\frac {70+80+\frac{76+67+90}{300}}{300}$ which shows that the first two papers each account for $\frac 13$ of the grade.  Your second has the first two papers accounting for $\frac 15$ of the grade.  If all five papers are supposed to be equally weighted, this is correct.
