Hi James ,
Please understand that a percentage figure is arrived at by dividing one value by another ; thus if cell A2 has the value 25 in it , and cell B2 has the value 75 in it , you can have the following formula in C2 : =A2/B2 ; formatting C2 as percentage will display 33.33%.
Now if you have a range of values in column A , from A2:A17 , and similarly values in column B , from B2:B17 , you can calculate the corresponding percentages in column C , from C2:C17.
The overall percentage in say C18 is not got by adding all the individual percentages from C2:C17 ; instead , you should use the following formulae :
In A18 : =SUM(A2:A17)
In B18 : =SUM(B2:B17)
In C18 : =A18/B18
Format C18 also as percentage.
Narayan