Addition Rule: P(A∪B)

Problem 1.1 • Visualize how the probability of a union is calculated

Set A
Set B
A ∩ B (Intersection)

Adjust Probabilities

P(A) 0.50
P(B) 0.40
P(A∩B) 0.20

Formula Breakdown

P(A) = 0.50
+ P(B) = 0.40
− P(A∩B) = 0.20
P(A∪B) = 0.70

💡 Why subtract the intersection?

When we add P(A) and P(B), we count the intersection twice — once in A and once in B. So we subtract P(A∩B) to correct for this double-counting. Watch the purple region in the diagram!