Probability Bounds

Problem 2.3 • Upper and lower bounds for P(A∩B) and P(A∪B)

📊 Visual Bounds

0 0.25 0.5 0.75 1

🔗 Intersection P(A∩B)

max(0, P(A)+P(B)−1) ≤ P(A∩B) ≤ min(P(A), P(B))
Lower: 0.00 Upper: 0.40

🔗 Union P(A∪B)

max(P(A), P(B)) ≤ P(A∪B) ≤ min(1, P(A)+P(B))
Lower: 0.50 Upper: 0.90

💡 Why These Bounds?

Upper bound for intersection: A∩B ⊆ A and A∩B ⊆ B
→ P(A∩B) ≤ min(P(A), P(B))
Lower bound for intersection: From inclusion-exclusion
P(A∪B) = P(A) + P(B) − P(A∩B) ≤ 1
→ P(A∩B) ≥ P(A) + P(B) − 1

⚙️ Set Probabilities

P(A) 0.50
P(B) 0.40

📐 Key Inequalities

• P(A∩B) ≤ P(A)
• P(A∩B) ≤ P(B)
• P(A) ≤ P(A∪B)
• P(B) ≤ P(A∪B)
• P(A∪B) ≤ 1
• P(A∩B) ≥ 0