#40 There are four lights
set by Paul Taylor
A machine has four lights labelled A to D, one of which is lit at any time. It also has a red button and a blue button. Pressing a button changes which light is on according to the arrows shown. (An arrow from a letter to itself means the light doesn鈥檛 change when that button is pressed.)
If light D is lit, how many different ways are there to press exactly three buttons and end up with A lit?
If the last button pressed was blue, what light cannot be lit?
If you can鈥檛 see the lights, what sequence of three buttons could you press to guarantee that either A or D is lit?
What sequence of five button presses guarantees that light A is lit?
Solution next week
#39 Game of logic
Solution
A red counter in the top right interior section (first image) shows that some cakes are new and wholesome, but not nice.
Some old cakes that aren鈥檛 nice or wholesome can be represented by a red counter in the bottom right exterior section (second image).
The red counter (last image) shows some cakes are wholesome, nice and new. The grey counters show no wholesome cakes are not nice.
Quick quiz #272
set by Bethan Ackerley
1 What name is given to the narrowing of a bodily passage or orifice, e.g. the spinal canal?
2 In the history of spaceflight, the statement that NASA's flight control must be "tough and competent" is known as what?
3 Which of the following isn't a pterosaur: Archaeopteryx lithographica, Quetzalcoatlus northropi or Dimorphodon macronyx?
4 Which gas forms about 78 per cent of Earth's atmosphere?
5 What was the first cancer-causing virus to be identified?
Quick quiz #272
Answers
1 Stenosis
2 The Kranz dictum
3 Archaeopteryx lithographica
4 Nitrogen
5 Epstein-Barr virus