Enigma 1172: Plant a tree
11 April 2016
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From New Scientist #2328, 2nd February 2002 [link]
George’s local council celebrated National Plant a Tree Year by planting four saplings in a public park. Unfortunately, a few nights later, vandals dug up one of the trees and cleared the ground leaving no evidence of where the tree had been. George has been asked to help.
The Mayor explained that the straight-line between the six pairs of trees had been carefully measured so that there were only two different distances. With three trees remaining where they had been planted, he asked it George could work out the original position of the fourth.
“No,” George replied, “I have identified four possible positions and I am still thinking”.
How many possible positions were there?