97. There are 5 parts that are indistinguishable in appearance, 4 of which are standard and of the same mass, and one is defective, differing in mass from the others. What is the minimum number of weighings on a balance scale without weights that are needed to find the defective part?
$\triangle$ Let's number the parts. Now try to figure out the weighing scheme presented below (Fig. 32).

As can be seen from this, it took three weighings to find the defective part.

Answer: in three.