Can you find the fake coin?
He tells you that exactly one of the 8 coins is counterfeit and that the counterfeit coin is heavier.
He then gives you a beam balance and an User Manual. You have never seen a beam balance before, so you open the user manual and find that it says:
You can place a coin or a group of coins on the two pans of the balance. You can find which side is heavier, if any or if their weights are equal.
What is the minimum number of times you need to use the balance to surely find the counterfeit coin?