Skill and automaticity with numbers is only part of the story. Students must also bring abstraction into play. This is also very commonly an uncon- scious process. There are huge numbers of choices for what to emphasize and what to exclude in real problems so as to focus on the core of what matters. Indeed, it is often far from clear what the core actually is. As was the case before, one has to practice to facilitate abstraction. How? One explores the situation, focusing on one area, then another, and accu- mulates sufficient data so that non-verbal tools in the brain can sort things out and focus on.
