Which example best illustrates a variable ratio schedule?

The example of slot machines in a casino best illustrates a variable ratio schedule because this type of reinforcement schedule delivers a reward after an unpredictable number of responses. In the case of slot machines, players must pull the lever (or push the button) multiple times, and each time is associated with a chance of winning, but the exact frequency of wins is variable. This means that the player may win after a few pulls or after many pulls, making the timing of the reinforcement unpredictable, which effectively keeps players engaged and playing.

Variable ratio schedules are known to create a high and steady rate of responding, as the uncertainty of when the next reward will come motivates individuals to continue the behavior. This is why gamblers often engage in repeated play, hoping for a win, as opposed to behaviors that offer a more predictable outcome, like studying for a set amount of time or completing homework assignments, which do not involve a chance-based reward system.