One wouldn’t believe how limited can thinking be sometimes.
If this is too easy for you though, look at the riddle with 13 coins.
Nine Coins
You were given nine same looking coins of which one is fake – weighs less. You can use even arm balance. How do you find out which coin is fake in two scalings?
Hint
How many coins do you leave aside?
Answer
Three coins on the left; three on the right; three aside. Left side goes down right side goes down or scales stay balanced. Now you know within which three coins the fake one is.
Now there are three coins – one left one right one aside...
