NRICH: Charlie's Delightful Machine

Can you work out how to switch the lights on?

Charlie’s Delightful Machine has four coloured lights. Each light is controlled by a rule.
If you choose a number that satisfies the rule, the light will go on.
Some numbers may turn on more than one light!

Start by exploring Level 1. Type in some numbers and see which lights you can switch on.
To start again with a new set of rules, click the Level 1 button.

Can you develop a strategy to work out the rules controlling each light?

Age 11 to 16 

You may wish to look at Shifting Times Tables before trying this problem.


Deductive Reasoning & Logical Thinking
Middle School, High School

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NRICH (University of Cambridge)

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Online Game

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