At the beginning of the semester your history instructor announced that you will have a test every three weeks until the end of the semester. What schedule of reinforcement was being used

Answer: Fixed interval

Explanation: Reinforcement schedule explains when instances of a behavior will be reinforced, that is the rate or timing of a reinforcement.

In the scenario above, the instructor is employing a fixed interval schedule with his decision to conduct a test every three weeks till the end of the semester. Fixed interval schedule are usually set, such that the date for upcoming reinforcements are already known. And it is not dependent on the outcome of the reinforcement.