2002 Math OSK, Number 2: Logic
Logic
Level
3
Bando always tells lies. One day, he said to his neighbor, Andi: "At least one of us never lies". From this information, we feel that...
Andi always tells truth
Andi never spoke
Andi always tells lie
Andi sometimes tells lie
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
1 solution
Since Bando always lies, the statement that at least one of them never lies is wrong for sure. In other words, it is evident that NONE of them never lies. This is only possible if Andi always lies or Andi lies occasionally. Whichever of these possibilities, we know the possibility that Andi never lies is out of the question. However, it is NOT conclusive whether Andi always or occasionally lies, so we conclude that he lies s o m e t i m e s (at least).