Fixed Ratio Schedule: A fixed ratio schedule is when reinforcement is provided after a fixed number of responses. For example, receiving a sticker for every 5 math problems solved correctly.
Variable Ratio Schedule: A variable ratio schedule is when reinforcement is provided after an unpredictable number of responses. For instance, winning prizes from a vending machine where the number of tries needed to win varies each time.
Fixed Interval Schedule: A fixed interval schedule is when reinforcement is provided after a fixed amount of time has passed since the last response. An example could be getting paid every two weeks for work done.