How much heavier is one cube than another?

Recall the difficulty students had last session, when they tried to weigh the cubes using a mixture of paper clips, steel washers, and counting bears.

• What did we decide to do this time?
• We decided to use just one measure, but which one was it?

Once the class has agreed what the class measure is (paper clip, washer, or bear), introduce the investigation question:

• How should we go about answering this question?

Let the students brainstorm some ideas. There will be talk about reweighing, comparing, “counting the difference,” and subtracting. Some students may suggest making a list or compiling a table or using a weight line. Entertain all such ideas, and help the class reach agreement that the task must begin with weighing all the cubes.