Answer:
Variable-ratio 
Step-by-step explanation:
Variable-ratio schedule: In psychology, the term "variable-ratio schedule" is described as one of the different reinforcement schedules in the operant conditioning theory which was proposed by B. F. Skinner. In the variable-ratio schedule, a specific response is being reinforced after an "unpredictable or unforeseeable number" of responses. However, the variable-ratio schedule creates a steady yet high rate in terms of response. 
Example: Gambling. 
In the question above, the given statement represents a variable-ratio schedule.