You have nine identical-looking coins. One of the coins is counterfeit and weighs less than the other coins.

Question

You have nine identical-looking coins. One of the coins is counterfeit and weighs less than the other coins. The only scale available is a balance scale. This scale lets you put any number of these coins on either side and will determine which side is heavier or if the sides are equal. Come up with a plan to use the scale exactly twice and find the counterfeit coin. Name the heuristic used.

Please help me as soon as possible!

Answer 1

Divide the coins into 3 groups of 3 coins.

Put 2 groups on scale to decide which group contains the counterfeit coin.

Put 2 coins of the group that contains the counterfeit coin on scale, you can find the counterfeit coin.