A fishkeeping enthusiast owns different species of fish. As some species are not compatible with others, he has acclimated them into fish tanks as follows:
Tank | Species |
Tank | |
Tank | |
Tank | |
Tank |
This morning, one of the fish tanks collapsed but luckily the fishkeeper was able to put the fish that fell on the floor back into the remaining tanks without any compatibility problems or the need to transfer some fish from one tank to another.
By looking at the compatibility table below, can you guess which tank broke ?
Species | is not compatible with |
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Relevant wiki: Graph Coloring and Chromatic Numbers
If the first tank breaks, species D cannot go elsewhere as it is incompatible with species K in tank 2 , with species E in tank 3 and with species L in tank 4 .
If the second tank breaks, species G cannot go elsewhere as it is incompatible with species H in tank 1 , with species C in tank 3 and with species F in tank 4 .
If the fourth tank breaks, species B cannot go elsewhere as it is incompatible with species A in tank 1 , with species I in tank 2 and with species E in tank 3 .
However, If the third tank breaks, species C and J can go into tank 4 and species E can go into tank 2 , hence the answer is t a n k 3 .