Jackie is always buying several packs of baseball cards, but only a fraction of those packs actually add new cards to her collection. She is likely on a __________

A) fixed-ratio.
B) variable-ratio.
C) fixed-interval.
D) variable-interval.

Jackie's behavior of buying several packs of baseball cards but only getting new cards in a fraction of those packs is indicative of a variable-ratio schedule of reinforcement. In this type of schedule, reinforcement occurs after a variable number of responses, which creates a high and steady rate of responding. In Jackie's case, she is motivated to continue buying packs of baseball cards because she never knows when she might get a new card to add to her collection.