Step 2: Define Events of interest. The outcomes in event A (coins match) and event B (first coin is heads) are checked in the tree diagram above Step 3: Compute outcome Probabilities. Since the coins are independent and fair, all -edge probabilities are 1/2. We find outcome probabilities by multiplying edge probabili- ties along each root-to-leaf path. All outcomes have probability 1/4. Step 4: Compute Fvent Probabilities. Now we can verify that Pr (An B) Pr (A) Pr (B):