Step 1: Identify the probability model.
This is a binomial distribution problem since there are a fixed number of trials and two outcomes (survive or not survive).
Step 2: Assign values.
Probability of survival \( p = 0.2 \),
Probability of not surviving \( q = 1 - 0.2 = 0.8 \),
Number of trials \( n = 5 \),
Required survivors \( r = 4 \).
Step 3: Apply the binomial probability formula.
\[
P(X = r) = \binom{n}{r} p^r q^{n-r}
\]
\[
P(X = 4) = \binom{5}{4} (0.2)^4 (0.8)^1
\]
\[
= 5 \times 0.0016 \times 0.8 = 0.0064
\]
Step 4: Final conclusion.
The probability that exactly four patients survive is
\[
\boxed{0.0064}
\]