Calculating a simple percentage

[#1]

Dear All,

  Please can any one solve my problem, as i am beginner to qlikview and have very little concept of expression and calculated fields in qlikview.

I have a below table under review,

Student_ID  Class_Room

A                    555

B                    666

C

D

E

can any one tell me the expression which shows % student in two classes.. ?

[#2]

Try This on the Expressions Tab:

(sum ([Class_Room]) / count (total [Student_ID]))