If cell and cell are blank do nothing

[amiina9100]

How to insert function if cell A and cell B are blank do nothing if they are number sum A+B ?

 

[Takae]

=if(and(a1="",b1=""),"",a1+b1)

 

[FDibbins]

Are they really blank (empty) or do they have a formula in them?

 

[amiina9100]

Are they really blank (empty) or do they have a formula in them?

They have formula in them

 

[amiina9100]

They have formula in them

and after that i need if cell is blank do nothing if it is higher than 3 show value 1 if it is lower show value -1, i just can't get it correct i don't know why