在Excel / Google表格中查找加权平均值

Question

I am trying to calculate student marks using a weighted average like in this sheet:

https://docs.google.com/spreadsheets/d/1E35005CEgqYlkRYE3IIqVnWTaOROD54L3eEt4nIo-8Y/edit#gid=0

B4:B13 has the equation to do it but I will have about 40 assignments which would made this long to type out.

I tried using SUMPRODUCT but there are 2 problems: 1. the weights are in every other column 2. if the mark is a blank cell then the weight for that assignment should be zero. (ex. see student 10 where assignment 1 weight should be zero and the overall grade should be 100%.

How can i use a formula to achieve this?

Answer 1

Try this:

=ArrayFormula(SUM(IF((MOD(COLUMN($D4:$Z4),2)=0)*(N(+D$1:$Z$1)<>0)*($D4:$Z4<>""),$D4:$Z4*$D$2:$Z$2/$D$1:$Z$1)*100/SUM(IF((MOD(COLUMN($D4:$Z4),2)=0)*(N(+D$1:$Z$1)<>0)*($D4:$Z4<>""),$D$2:$Z$2))))

If you want a formula that will grow with extra columns added then use this monster:

=ArrayFormula(SUM(IF((MOD(COLUMN($D4:INDEX(4:4,MATCH(1E+99,$2:$2))),2)=0)*(N(+D$1:INDEX($1:$1,MATCH(1E+99,$2:$2)))<>0)*($D4:INDEX(4:4,MATCH(1E+99,$2:$2))<>""),$D4:INDEX(4:4,MATCH(1E+99,$2:$2))*$D$2:INDEX($2:$2,MATCH(1E+99,$2:$2))/$D$1:INDEX($1:$1,MATCH(1E+99,$2:$2)))*100/SUM(IF((MOD(COLUMN($D4:INDEX(4:4,MATCH(1E+99,$2:$2))),2)=0)*(N(+D$1:INDEX($1:$1,MATCH(1E+99,$2:$2)))<>0)*($D4:INDEX(4:4,MATCH(1E+99,$2:$2))<>""),$D$2:INDEX($2:$2,MATCH(1E+99,$2:$2))))))

It will find the last column in which there is a number in row 2 and use that as its ending column.