Sum function for non numeric choice field?

Hey all, 

How do I sum non numeric values using the sum function and  setting values using the if function within? 

Here's my example formula, it works if it only has one value assigned, but when I add  another field to assignment, it doesn't add it to the sum. (I'm trying to assign a number value to the multiple choice questions they get correct)

Works:    sum(If(contains(Question1,"a."),1,0))

Doesn't work:   sum(If(contains(Question1,"a."),1,0),If(contains(Question2,"a."),1,0))

What am I missing?  It's probably a comma or something like that.