SUMIF to sum cells only if other corresponding cells contain a number

Question

I'm trying to solve this:

I'm playing around with the sumif and sumifs function but I can't seem to figure it out.

It's important to sum up all cells of B only, and only if the corresponding cells A have a number in it (any number will do). This condition is important, because some cells are empty, some have random strings in it, some are marked with "N.A.", etc.

Answer 1

If the column A numbers are strictly non-negative:

=SUMIF(A:A,">=0",B:B)

If that column may contain negative numbers:

=SUM(SUMIF(A:A,{">0","<"}&0,B:B))

Note that any numbers stored as text in column A will not be considered, neither by these solutions nor that given by zx8754.

Regards