1. The problem asks for the probability of heads appearing on the 5th toss of a fair coin, given that tails appeared on the first four tosses. 2. A fair coin means the probability of heads or tails on any toss is $\frac{1}{2}$. 3. The coin tosses are independent events, so the result of previous tosses does not affect the probability of the next toss. 4. Therefore, the probability of heads on the 5th toss is simply $\frac{1}{2}$. 5. The previous four tails do not change this probability. **Final answer:** $\frac{1}{2}$