Probability and non-probability sampling you meant?The difference between nonprobability and probability sampling is that nonprobability sampling does not involve random selection and probability sampling does. At least with a probabilistic sample, we know the odds or probability that we have represented the population well.
However, I'm not entirely sure in terms of math. If the probability of something happening was, let's say, 73%, the non-probability sounds like it states the chance of that something not happening, which would be 27%. But this is just an assumption, don't take my word for it.