Which of the following is an example of a fixed ratio schedule of reinforcement?

In a fixed ratio schedule of reinforcement, a specific number of responses must occur before a reward is given. This means that the reward is contingent upon a set amount of work being completed, creating a consistent pattern that reinforces the behavior at fixed intervals of performance.

In the correct option, Sara earns a break after typing exactly 30 words. This is a clear example of a fixed ratio schedule because there is a defined number of responses (30 words) required to earn the reinforcement (the break). Her performance is directly linked to this precise quantity, and she knows that upon reaching that threshold, the reward will be granted.

This clarity in the number of responses needed to achieve the reward is what distinguishes this option from others that do not specify an exact fixed number necessary for reinforcement. Other approaches, like varying the number of words typed or providing breaks based on averages or ranges, do not fulfill the fixed requirement that characterizes a fixed ratio schedule.