three columns: H,D,C
every entry in D and C is a number
entries in H, which are not numbers, are blanks

the problem is to sum the product of entries in C and D that correspond
to blank entries in H

SUMPRODUCT(if(isblank(H3:H20),1,0)*C3:C20*D3:D20) computes an answer,
but it is wrong; it sums the unconditional product of entries in C and
D

inserting the above into function computes an answer, and it is correct

why doesn't my formula compute correctly?

John