Count rules for three Yes/No conditions

Scenario. A bicycle-sharing service checks three things before unlocking a bicycle:

• Does the rider have a valid pass? Yes or No
• Is a bicycle available? Yes or No
• Is the station open? Yes or No

Every combination of answers is possible. For example, a rider may have a valid pass even when no bicycle is available.

A raw combination contains one answer for every condition. A full decision table begins with one decision rule for each raw combination. How many rules are needed before cases with the same result are combined?

• 6 rules
• 8 rules
• 9 rules
• 16 rules