Excel Condition

I have column A with some numbers and column B, where some cells are empty and some cells contains '+'. And I want to sum cells from Column A, but only cells in rows where B column contains '+'.

For example:

A    B
1    +
2    
3    +
4    

So I want to sum 1 and 3 and get 4.

Can anybody help me?

Answer

SUMIF should do it, as in:

=sumif(B1:B4,"+",A1:A4)