ISBLANK in an IF statement

[Becky]

How do I write this IF statement/formula in cell A3:

cell A1 has a number in it.
cell A2 is blank, but will eventually have a number in it.
cell A3 is blank, but will display the sum of A1+A2 AFTER
there is an entry made in A2. I want A3 to remain blank
until there is an entry made in A2.

Whenever I try to use =isblank in my IF formula, the
result comes back as "invalid". I've tried everything.

Is what I'm asking for possible? Thanks!!

 

[Dan E]

Becky,

Try
=IF(A2="","",A1+A2)

Dan E

 

[Paul]

How do I write this IF statement/formula in cell A3:

cell A1 has a number in it.
cell A2 is blank, but will eventually have a number in it.
cell A3 is blank, but will display the sum of A1+A2 AFTER
there is an entry made in A2. I want A3 to remain blank
until there is an entry made in A2.

Whenever I try to use =isblank in my IF formula, the
result comes back as "invalid". I've tried everything.

Is what I'm asking for possible? Thanks!!

Either
=IF(ISBLANK(A2),"",A1+A2)
or
=IF(A2="","",A1+A2)

 

[Dave R.]

I think you may be putting hte isblank in the wrong spot, try

if(isblank(a2),"",a1+a2)

 

[Harlan Grove]

...
...

cell A1 has a number in it.
cell A2 is blank, but will eventually have a number in it.
cell A3 is blank, but will display the sum of A1+A2 AFTER
there is an entry made in A2. I want A3 to remain blank
until there is an entry made in A2.

...

Even though A1 may have a number in it, in the off chance it doesn't but A2 does
contain a number, would you still want the sum? If not, then another alternative
would be

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