First, divide 27 coins into three parts according to 9 coins in each part, and then put any two coins on the balance. If the balance is balanced, the counterfeit money is in the one that has not been taken. If not, the counterfeit money is in the light color. This is the first weighing. Then, divide the nine coins with counterfeit money into three parts by the same method for the second time, and do it again by the method used for the first time, and you will know that the counterfeit money is in three parts.