Problem:

When I enter the following equation into a cell with a blank in cell
CH12 or CH13 I get the correct answer (the sum of the cells with
numbers in them) but when there is a blank in cell CH14 I get an
incorrect answer (in the form of a clank cell).

=IF(AND(ISNUMBER(CH12:CH14)),SUM(CH12:CH14),"")

Does anyone have any suggestions?

Thanks,
Elaine