Crossing River Puzzle Solution - 25 August
There is a river to cross using a river raft and there are eight people (father, mother, policeman, thief, 2 daughters and 2 sons). No one knows to operate the raft except the adults and also excluding the thief. Only two people can go in the raft at a time. The raft should keep coming back and forth in order to pick and drop the people.
Rules to be followed:
Father: the father cannot stay in the raft or outside the raft without the presence of the mother.
Mother: the mother cannot stay in the raft or outside the rat without the presence of the father.
Thief: the thief is not allowed to stay with any of the family member unless there is a policeman.
Policeman: the policeman can travel with anyone.
2 sons and 2 daughters: they are not allowed to travel in the raft without the presence of any adult. They cannot either travel in the presence of only thief without the policeman. The sons cannot be with their mothers without their fathers supervision. The daughters are not allowed to be there with their fathers without the supervision of their mothers. But the daughters and the sons can be left unsupervised (as long as the other rules are applied).
What is the sequence that the people should follow in order to cross the river through the raft keeping in mind all the rules?
The rules are applicable not only in the raft but also outside the raft.
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SolutionThe following letters are assigned to respective person. Father (F), mother (M), thief (t), policeman (p), sons (s1 & s2), daughters (d1 &d2). And imagine that they are starting from the eastern side of the river |.
During the first trip, t will be taken across the river by P. The rules are still kept. After leaving t, P will return. So now it is t | P, M, d1, d2, s1, s2, F
In the second trip, d1 will be taken by P across the river and leave her back. But t will be brought back. Now it is d1 | P, F, M, d2, s1, s2, t
During the third trip, d2 will be taken across the river by M and will return. Now it is d1, d2 |P, M, F, t, s1, s2
In the fourth trip, F and M will cross the river together and M will stay back and F will return. Now it is M, d1, d2 |P, F, t, s1, s2
During the fifth trip, t will be taken across the river by P and M will return. So now it is P, d1, d2, t |M, F, s1, s2
In the sixth trip, F and M will go across the river and F will be back. Now it is P, M, d1, d2, t |F, s1, s2
During the seventh trip, s1 will be taken across the river by F and P will come back with t. now it is M, F, d1, d2, s1 |P, t, s2
In the eighth trip, s2 will be taken across the river by P, and then he will return. Now it is M, F, d1, d2, s1, s2 |P, t
In the ninth trip which is final t will be taken across by P.
This is by the assumption that the thief is left unsupervised. The rules do not mention that anyway.
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