Theory versus experiment.

Theory says P(7) with two dice is ⅙. Does an experiment agree? Let us compare theoretical probability and experimental probability.
7 came up 17 times out of 100: 0.17. Theory: 1/6 ≈ 0.167. Very close!
Small experiments can be far from theory. Large experiments get closer. This is called the law of large numbers.
A simulation uses a simple model. Three coins can stand for three children. Repeat many times to estimate probabilities.