Hard to match qua refernces the verbal description you give with the
formulas you post. That said:

=E16/COUNTIF($C$29:$C$33,"M")

can be re-expressed to avoid #DIV/0! as

=E16/MAX(1,COUNTIF($C$29:$C$33,"M"))

Marie1uk wrote:
Can I have advice on how to make the following formulae return a blank
cell instead of a #div/0 error when the first reference cell in the
formula is blank or 0?

=E16/COUNTIF($C$29:$C$33,"M")

in cell J21: =COUNTIF($H$42:$H$426,"A~*")/COUNT($J$42:$J$426)

in cell F25: =SUM(J21:J24)

Another rather annoying thing is that in cell A9 and A13 there is a 0
displayed. The formula in cell A9 is =E147 and in A13 it is E287. There
is absolutely nothing in E147 or E287. I have tried everything I can
think of to get A9 and A13 to remain blank instead of displaying a 0 (I
may have typed something into E147 and E287 at one time to test it). Any
ideas how to get rid of these zeros?