Simulations are used to relate probabilities by modeling complex situations as simple experiments. The document discusses using simulations on calculators and smartphones to model probabilities. It provides an example of simulating a baseball player's batting average over 10 at-bats. The simulation is run 25 times to determine the probability of getting exactly 3 hits is 8/25. The document also discusses using coins, cards, dice, and spinners to simulate different probability ratios like 1:2, 1:4, and 1:6. It concludes with assigning problem set questions from the textbook.