sum only if there is a value in cells

[Geo]

I have the following formula:
A3=SUM(A1+A2)
Is there a way so that A3 only sums if there is a value in both cells and
not if there is text?
The values are hours and minutes.

 

[Luke M]

=IF(AND(ISNUMBER(A1),ISNUMBER(A2)),A1+A2,"")

 

[T. Valko]

=IF(AND(ISNUMBER(A1),ISNUMBER(A2)),A1+A2,"")

=IF(COUNT(A1:A2)=2,A1+A2,"")