If there are only 1 defective products, weighing n times can distinguish at most 3 n. Firstly, the tested object is divided into three equal parts (if it cannot be divided equally, the difference of the quantity of each part is 1 as far as possible), and each part is weighed to obtain the defective products in the three groups; Divide them into three groups and weigh them separately, and so on. After weighing n times, the defective products in 3 n projects can be identified. For example, it is known that there are 1 defective products in 27 objects to be tested, and the location of the defective products can be known by weighing for three times.