First, we have the item 16. Divide them into three groups and get 556 points. Put five or five groups on the balance or self-made balance to see if they are balanced. If it is balanced, then the defective product is in six. Similarly, divide six into three parts and put them on the balance for observation. On the other hand, group and find out the defective products according to the previous steps.

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If, it is unbalanced. Then, there are defective products in the heavy five. At this time, divide the five into 22 1. Similarly, put 22 on the balance and see if it is balanced. The process is similar to the first step.

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Finally come to the conclusion that it will take at least three times to find out. Here, we use the branching method. When the defective products are light, we can also judge according to this model. This way is clear and easy to understand.

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