Statistics like the op said. If you are expecting your decay products from an interaction to be 20% X and 80% Y but after 100 billion attempts which should have

Statistics like the op said. If you are expecting your decay products from an interaction to be 20% X and 80% Y but after 100 billion attempts which should have averaged out to the expected outcome you instead get 21% X and 79% Y something in your calculation is wrong.