Ok, lets see if i can explain this one well enough...

I have 3 columns, A,B and C. In these columns are numbers. In Column D
I want to apply the following formula: =A1+MAX(B1/365,C1/6)

This works however the problems arrise as there are some cells in
columns A:C which are blank or have text not numbers. I tried to fix
this with this formula: =ISNUMBER(A1:C1),A1+MAX(B1/365,C1/6)

This works however if there is no number in any one of the three cells
it returns a "FALSE" error. I would prefere it to display nothing, ie
"". But i can't seem to do this.

Other more complex problems: if there is one number in either column B
or C i would like it to complete the formula using this number. There
must always be a number in column A. If there is no number in A then
the result should be blank.

example:

A B C D
4 6 7 calculate
6 7 Nothing
text 6 7 Nothing
4 text 7 calculate
4 Nothing
4 text text Nothing
4 text Nothing


Hopefully someone can help me. It is driving me crazy!

Jon Scott