My students have to understand dependent probability with and without replacement. To help with the understanding of this, I created this activity with buttons. As students work through the activity, they can take out buttons as the problem states to see why the denominator changes.
You can buy a large container of buttons from Michael's or Hobby Lobby for pretty cheap. Then I put the same number of each color of buttons in snack-sized baggies to make the grading easier. My students work in pairs so I only need half as many baggies as students in the class.