Column multiplication can be used to solve practical problems, and the number of people who only do the first problem, only do the second problem and do both correctly is set as different unknowns, and the equations are listed according to the meaning of the problems to solve.
The decomposition process is as follows:
Solution: Suppose that X people did the first question correctly, Y people did the second question correctly, and Z people did both questions correctly.
X+Z=33，
Y+Z=28，
X+Y+Z=45，
Get z = (33+28)-45 = 16 people.
A: There are 16 people who answered both questions correctly.
Extended data:
Under the condition that all students correctly answer at least 1 question, we can get that the number of people who correctly answer at least 2 questions is 16.
But if a student does both questions wrong, we can't find the answer.
Suppose there are X people who only answered the first question correctly, Y people who only answered the second question correctly, Z people who answered both questions correctly and A people who answered both questions incorrectly.
X+Z=33，
Y+Z=28，
X+Y+Z+A=45，
Z can't be found because A is unknown.