We are looking for the probability that a customer carries at least one of the two credit cards (Rupay or Visa). This is the union of two events, so we use the formula for the union of two sets:
\[ P(A \cup B) = P(A) + P(B) - P(A \cap B) \]
Where:
Substitute the given values into the formula:
\[ P(A \cup B) = 0.31 + 0.44 - 0.18 = 0.57 \]
Thus, the probability that a customer carries at least one of the two credit cards is 0.57.