One way:

=IF(COUNT(C13:E13)<3,"",AVERAGE(LARGE(C13:E13,{1,2 })))


Note, with the formula you're using now, someone who got two or more of
the same low grades would have them BOTH/ALL dropped.


In article ,
Naomi wrote:

I have a formula that takes a array that includes number grades, drops the
lowest grade and averages them. If there is no data in cell yet i get a
#DIV/0! error is there a way to copy this formula to following cells without
data in them yet and not get this error. The formula Im using is:
=AVERAGE(IF(C13:E13<MIN(C13:E13),C13:E13))