Make a table of all the possible sums that we can make (sums are in black ink)
There are 6*6 = 36 sums in the table. Of which, there are 3 copies of 10 (formed by 4+6=10,5+5=10,6+4=10). So that makes 36-3 = 33 copies that are not a sum of 10.
Divide the number of copies that aren't ten (33) over the total number of sums (36) to get . Don't forget to reduce as much as possible.
The answer as a fraction is
If you need the answer in decimal form, then use a calculator to get this approximate result (rounded to 4 decimal places)