Katrina is trying to put a dollar bill into a vending machine in her office. sometimes the machine will take a dollar bill on the first try, other times it can take up to five or six tries before the dollar bill is finally accepted. in this example, inserting a dollar bill into the vending machine is reinforced on

An intermittent reinforcement schedule.

Explanation:

Intermittent reinforcement schedule may be defined as the schedule that produces the stable state that helps the individual to respond and maintained for long period of time.

The response occurs still for the sometime until it is not reinforced. The new respond begins after sometime. As Katrina puts dollar bill and the machine shows different response and this maintains for the long time. This clearly represents  intermittent reinforcement schedule.