12. (6 points) There are 9 steel balls, 8 of which weigh the same, and one is slightly lighter than the other 8. Using a balance scale, what is the minimum number of weighings required to find the lighter steel ball?


【Solution】Solution: (1) Divide the 9 steel balls into 3 groups evenly, place two of the groups on the balance. If the weights are the same, the lighter one is in the third group; if the weights are different, the lighter one is in the group on the higher side of the balance;
(2) Take the group with the lighter steel ball, and place two of them on either side of the balance. If the balance is even, the remaining one is the lighter one; if the balance is uneven, the one on the higher side is the lighter one. In this way, using the balance 2 times will definitely find the lighter steel ball.

Answer: Using a balance, it takes a minimum of 2 weighings to find the lighter steel ball.