Charlie's Delightful Machine

The problem could be used to reinforce work on recording and describing linear and quadratic sequences.
 

Possible approach

This task will require students to have access to computers. If this is not possible, Four Coloured Lights provides students the opportunity to make sense of numerical rules without the need for computers.

Shifting Times Tables is a problem about linear sequences that could be used to prepare students for the thinking required in this problem.

 

Begin the lesson by dividing the board into two columns, one headed with a tick and the other headed with a cross.

Ask students to suggest numbers, and write each suggestion in the appropriate column according to a rule of your own choice. 

Here are some suggestions for rules:

Once the class have tried the activity with a couple of rules, move on to the main task.

To introduce the main task (Level 1), show the interactivity and demonstrate entering a couple of numbers to see what lights up. Make sure students understand that more than one light can light up at once, and that each light is governed by its own rule.

Level 1 rules are linear sequences of the form $an+b$, with a and b between 2 and 12.

Students could then work in pairs at a computer, trying to light up each of the lights. Challenge them to develop an efficient strategy for working out the rules controlling each light.

While the class is working, note any particularly good ways of recording or working systematically, and highlight them to the rest of the class.

Bring the class together to share insights and conclusions before moving on to A Little Light Thinking, in which students are invited to find sequences that turn several Level 1 lights on simultaneously.

Key questions

Which numbers will you try first?

Possible extension

Level 2 rules are quadratic sequences of the form $an^2+bn+c$ with a=0 or 1

Level 3 rules are quadratic sequences of the form $an^2+bn+c$ with a=0, 0.5, 1, 2 or 3.

Level 3 sequences can be used as a starting point for some detailed exploration into graphical representations of quadratic functions.