1) The document provides a sample space and tree diagram showing the 16 possible combinations of 4 children being boys or girls given a 50% probability for each birth. 2) It then calculates that the probability of having at least 3 girls is 5/16 or 31.25% based on there being 5 combinations with at least 3 girls. 3) Finally, it calculates that the probability of having exactly 2 boys is 6/16 or 37.5% based on there being 6 combinations with exactly 2 boys.