Hmm, this daft/simple formula has got me stumped.

I have a simple table with column C that contains numeric values, and column D that contains date values.

All I want to do is a calculate the SUM of cells in column C that do not have a date value in column D.

Something like this... but obviously this does not work, possible as the evaluated data type is a date. Any ideas?

=SUMIF('TRAVEL ADVENTURES'!D3:D105,"NOT(ISBLANK)",'TRAVEL ADVENTURES'!C3:C105)