Monday 5 October 2009

Interesting Riddle

This riddle was given by Kaplan's lecturer
She always give us a riddle whenever she starts a class
Last week was an interesting one:)

Here is some sharing:)

Imagine you are on your way to a destination. You reach a road junction where you can turn left or right. You know that only one of the two roads will leads you to your destination, but you got no ideas which one is the correct one. You see two twin-brothers standing at the road junction and both of them will know the way to your destination. However, one of them always tells the truth and another one always tells lies. How can you find out the way to your destination if you are only allow to ask one question to one of the two brothers? (what question would you ask?)

Have a guess:) it's quite hard but it make sense:) There is absolutely no trick on this!

*Will put the correct answer in comments tomorrow night:)

5 comments:

Dominic said...

which road would your brother ask me to take?

JC said...

nearly there... but not entirely right:)

no online searching ah!

HuiHui said...

answer answer answer answer answerrrrrr...i cant wait edy...ahahahaha...

dom, if u ask that question, which "bro" u going to ask and which u know he is the 1 who telling truth or lie???

JC said...

So here is the Answer for the riddle!
Some might feel how does this work? It’s a bit unbelievable but... trust me.. You just have to believe this is the only answer!
So here you go!
The question that you should ask is (to either one of the brothers):
“If I ask your brother is this the right road to my destination, would he says YES or NO?” (point to either one of the road before you ask)
If he answers “NO” then the road that you pointed is the correct way! If he answers “YES” then you should choose another road to your destination!
Explanation: There are four possible cases:
If you ask the question to the truth-telling brother, and the road that you pointed is the correct one. The truth-telling brother knows that his lying brother would lied to you and say it’s not the correct one, and so he answers "No".

If you ask the question to the truth-telling brother, and the road that you pointed is the wrong way. The truth-telling brother knows that his lying brother would lie to you and say it’s actually correct, and so he answers "Yes".

If you ask the question to the lying brother, and the road that you pointed is the correct one. Even thought the lying brother knows that his truth-telling brother would say YES-it’s the correct one, but he will still lies to you and say "No".

If you ask the question to the lying brother, and the road that you pointed is the wrong way. The lying brother knows that his truth-telling brother would say that No-the road is not the right way, but he will still lies to you and say "Yes".

GET IT?

JC said...

Don't bother the Dom!

He search the answer online!