Puzzle #45: Beetles on a clothes line
9 February 2020
Posted by on
From New Scientist #3268, 8th February 2020 [link] [link]
Peg beetles are a rare species with rather odd behaviour. As any peg beetle expert will know, these beetles always walk at 1 metre per minute, and when two beetles meet, they immediately reverse direction.
Six peg beetles are on a 2-metre-long clothes line, some walking left to right and others right to left (as the diagram shows). As we join the action, beetle A is at the left-hand end of the line and walking towards the right, while beetle F is at the right-hand end, walking left.
When a beetle reaches the end of the clothes line, it drops off onto the ground.
Which two beetles will be the last to drop off the clothes line, and how long will it be before that happens?