Solution: The cost of each set of tables and chairs is X yuan.

The original profit is 60( 100-X)

The profit after buying more is 72( 100-3-X).

Get the equation

60( 100-X)= 72( 100-3-X)

X=82

Extended data

Solve the equation:

1, carefully examine the question and thoroughly understand the meaning of the question, that is, find out the known quantity, the unknown quantity and their relationship; Use letters (such as X) to indicate the unknowns in the question.

2. Find the equation relationship according to the meaning of the question (this is a key step).

3. According to the equation relationship, correctly list the equations, that is, the listed equations should satisfy that the quantities on both sides should be equal; The units of algebraic expressions on both sides of the equation should be the same; The conditions in the problem should be fully utilized, and none of them can be omitted or reused.

4. Find the solutions of the listed equations.

5. Write the answers clearly and completely after the exam. The test required here should be that the solution obtained from the test can not only make the equation valid, but also make the application problem meaningful.