12 balls, one defective product, with a fixed weight, called three times, how to determine which defective product is

RT

Baidu's solution:

Make the ball a number, first 1, 2, 3, 4, 5, 6, 7, 8, said, if the balance, the defective product is in 9, 10, 11, 12, and then called twice, it is easy to find out.
If not, 9, 10, 11, and 12 are genuine products. Remember the severity of the two sides. If the left side is heavy (and so on), take 1, 2, 3, 5, 6, 7 to the left, and put 9, 10, 11 on the right.
At this time, if the left side is still heavy, the defective product is 4 or 8, and it will be found again.
At this time, if the right side is heavy, the defective product is in the range of 5, 6, and 7, and the defective product can be judged to be light. Once again, you can find the defective product.
At this point, if the balance is reached, the defective product will be in the range of 1, 2, 3, and the defective product can be judged to be heavy. the defective product can be found once again.
There are many methods.

The light side may only be light, and the heavy side may only be heavy