Step 1: Understanding the Concept
E = {X is prime} = {2, 3, 5, 7}. F = {X < 4} = {1, 2, 3}. The union rule is \(P(E \cup F) = P(E) + P(F) - P(E \cap F)\).
Step 2: Probabilities
\(P(E) = 0.23 + 0.12 + 0.20 + 0.07 = 0.62\).
\(P(F) = 0.15 + 0.23 + 0.12 = 0.50\).
\(E \cap F = \{2, 3\}\), so \(P(E \cap F) = 0.23 + 0.12 = 0.35\).
Step 3: Union
\[ P(E \cup F) = 0.62 + 0.50 - 0.35 = 0.77 \]
Option (C), 0.35, is only the probability of the common part E and F both occurring.
Final Answer:
The probability is 0.77, option (B).
\[ \boxed{0.77} \]