You are testing an e-commerce system The system accepts four different types of Credit Cards; each card has its own rules for valid and invalid numbers. The following is a portion of the Decision Table for Order Management.:

The combination of the conditions Valid Card Number (NO) + Purchase Approved (YES) is not feasible.
You wish to perform a test which completely covers all the combinations of equivalence partitioning tor the different types of credit card, according to the rules shown in the above Decision Table How many test cases do you need?
Correct Answer: C
The combination of the conditions Valid Card Number (NO) + Purchase Approved (YES) is not feasible, as a purchase cannot be approved with an invalid card number. Therefore, this combination can be ignored in the equivalence partitioning for the different types of credit card. Each type of credit card has two valid equivalence partitions: Valid Card Number (YES) + Purchase Approved (YES) and Valid Card Number (YES) + Purchase Approved (NO). Each type of credit card also has one invalid equivalence partition: Valid Card Number (NO) + Purchase Approved (NO). Therefore, to cover all the combinations of equivalence partitions for the four types of credit card, we need 4 x (2 + 1) = 12 test cases.
A, B, and D are incorrect answers. A implies that there are two equivalence partitions for each type of credit card, which is not true as there are three. B implies that there is only one equivalence partition for each type of credit card, which is not true as there are two valid ones and one invalid one. D implies that there are four equivalence partitions for each type of credit card, which is not true as there are only three.