Difficulty: Taxing

Gillian is running the lights for a big musical. The spotlight has a rotating circle of six frames that she puts filters (like cellophane) in, allowing her to change the light’s colour.

The controls are simple. you can:

  • Turn the light on or off,
  • Rotate the frame one spot clockwise, or
  • Rotate the frame one spot anticlockwise.

For this show, the first three frames are red. The remaining three frames have no filter, so they produce white light.

During the show, Gillian turns on the spotlight, expecting it to be white. But instead, it’s red! Someone must have rotated the frame without telling her. Luckily, the scene is short, and she can bring the lights down.

Gillian doesn’t have time to go up into the rig and look at the light. She can’t turn it on to see what colour it is, as it would ruin the performance. And it’s getting close to the climax of the show! She really needs a white spotlight up next.

Can you work out how to make sure the light is white?

Scroll down or click for a hint, or the answer!


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Brainteaser hint

Try drawing the circle of frames. Do you notice any patterns with the white and red frames?

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Brainteaser answer

The first three frames are red and the remaining three are white. If you draw the circle of frames, you’ll notice that opposite every red frame is a white one.

The frame Gillian started on is red, so she just needs to go to the opposite frame. She can do that by going clockwise three spots, or anticlockwise three spots!

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