Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

Solutions for Session 3, Part A

See solutions for Problems: A1 | A2 | A3

 Problem A1 The inputs 12 and 8 each lead to the output 4. If you only knew that the output was 4, it would be impossible to determine which of 12 and 8 was the correct input.

Problem A2

Some examples:

 • Driving directions. Telling someone how to get somewhere usually allows them to figure out how to get back (if there are no one-way streets involved). In particular, to drive back you must take each road the opposite direction, and in reverse order (last road first). • Packing and unpacking. Especially with commercially shipped packages, it can be difficult to re-pack a box without knowing where things were located before you unpacked it. • In mathematics, many algebra problems involve "undoing" steps. For example, if 3x = 12, you can find x by undoing the multiplication step.

 Problem A3 Lots of things can't be undone easily, like throwing a water balloon, using gasoline in a car engine, or exploding fireworks.

 Session 3: Index | Notes | Solutions | Video