What is the Japanese river iq test?

Answer 1

This is a puzzle involving taking individuals across a river two at a time on a raft. It is similar to another puzzle using corn, a chicken, and a fox, in that some groups of people cannot be left by themselves on one side of the river, necessitating several specific trips to cross, and recross the river.
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There are 8 individuals that have to cross:
a mother
a father
two sons
two daughters,
a criminal
a policeman
The raft can only hold two people at a time, and only the mother, father and policeman can operate it. The following stipulations are made:
A) the mother cannot be left alone with either of the sons
B) the father cannot be left alone with either of the daughters
C) the criminal cannot be left with anyone unless the policeman is also present.
This obviously requires a number of crossings (5) by the policeman and criminal.
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The solution requires 12 round trips with the following pairs:
1) Policeman takes criminal across (secures him) / Policeman crosses back
2) Policeman takes one son across / Policeman and criminal cross back
3) Father and second son cross / Father crosses back
4) Father and mother cross / Mother crosses back
5) Policeman and criminal cross / Father crosses back
6) Father and mother cross / Mother crosses back
7) Mother and one daughter cross / Policeman and criminal cross back
8) Policeman and second daughter cross / Policeman crosses back
9) Policeman and criminal cross