Thank you Glenn, now I have a question.
How I can do this in excel?
I have a sequence of 15-0 15-0 0-15 0-15
The probability of getting 15-0 is 2/3 because the last results are not equal to 15-0
so I think the formula can be:

find in an array of cells from B4 to F4 last value(or a value I specify) and if a last value repeats, sum how many times it repeats