I have 8 subjects in my course. Following are the data of attendance in each subject.
Subjects Attended/Total Percentage
1 10/29 34.48 %
2. 23/23 100.00 %
3. 18/19 94.73 %
4. 18/19 94.73 %
5. 18/19 94.73 %
6. 18/19 94.73 %
7. 18/19 94.73 %
8. 18/19 94.73 %
------------------------------------
Total 141/166 87.85 %
But If I am calculating percentage only for 141/166 = 84.93 %
There is a big difference => 87.85 - 84.93 = 2.92 % for same attendances
So this difference is because of not rounding off correctly or my method is incorrect?
Best Answer
No. When you get $84.93\%$ you are considering each term with its weight (subjects have different totals): $$WM=\frac{\sum_{i=1}^8 \%_i \times \text{total}_i }{\sum_{i=1}^8 \text{total}_i}, $$ while in $87.85 \%$ you're calculating $$AM=\frac{1}{8}\sum_{i=1}^8 \%_i.$$ That's the difference between weighted arithmetic mean and arithmetic mean. The choice is up to you.