Imagine that there are twelve coins in front of you. They are exactly the same size and shape, but one is either lighter or heavier than the other 11. To determine which coin is the odd one out, you are allowed to use a scale exactly three times. How do you find the unique coin while figuring out whether it is heavier or lighter than the other coins?
I have two coins in my pocket that add up to the value of 30 cents. One of them is not a nickel. What two coins do I have in my pocket? (This riddle uses US currency, which means that the only coins available for the riddle are: penny (1c), nickel (5c), dime (10c) and quarter (25c))
The answer is a quarter and a nickel. Some might angrily retort that one of them should not be a nickel and that is correct. One of them is not a nickel, the other one is. We commonly place such simple yet seemingly unbreakable barriers in our minds. If you cannot solve a problem, take a step back and try to look past the barriers.