Brain Gymnastics 2
Some villagers were to visit another village. So the story runs. On their way, the road divided into two roads. There were two brothers who knew the true road. One brother always told the truth, the other always told a lie. Only one question may be asked to only one of them. The villagers couldn’t decide which road was the road to be taken. So they returned and asked Abu Nawas for help.
On the same spot again, Abu Nawas questioned one of the twin brothers. After hearing his answer Abu Nawas then was assured which road was the right one.
“How could you know this?” the people asked him.
“Well, that’s easy.”
Can you guess what he asked to know which road is the road that should be taken?
This was what Abu Nawas asked:
“What would your brother tell me whether this road is the true road?” Suppose it was the truth teller - if this is the true road – he would say:“my brother (the lier) would say ‘this is the wrong road’.” Than that is the right road since his brother always lied.
Suppose it was the lier instead who answered, he would also say “my brother –the truth teller - would say ‘that is the wrong road’.” As he always lies. Then again, this is the true road, not the other.
So that certainly must be the true road.
If the answer was: “Yes, this is the true road.” Then the true road is not this road, it must be the other one.
January 2011
Some villagers were to visit another village. So the story runs. On their way, the road divided into two roads. There were two brothers who knew the true road. One brother always told the truth, the other always told a lie. Only one question may be asked to only one of them. The villagers couldn’t decide which road was the road to be taken. So they returned and asked Abu Nawas for help.
On the same spot again, Abu Nawas questioned one of the twin brothers. After hearing his answer Abu Nawas then was assured which road was the right one.
“How could you know this?” the people asked him.
“Well, that’s easy.”
Can you guess what he asked to know which road is the road that should be taken?
This was what Abu Nawas asked:
“What would your brother tell me whether this road is the true road?” Suppose it was the truth teller - if this is the true road – he would say:“my brother (the lier) would say ‘this is the wrong road’.” Than that is the right road since his brother always lied.
Suppose it was the lier instead who answered, he would also say “my brother –the truth teller - would say ‘that is the wrong road’.” As he always lies. Then again, this is the true road, not the other.
So that certainly must be the true road.
If the answer was: “Yes, this is the true road.” Then the true road is not this road, it must be the other one.
January 2011
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