Draw two intersecting circles. Suppose circle A is the number of students who do the first question correctly, and circle B is the number of students who do the second question correctly. The intersecting part is named C, that is, the number of students who answered the two questions correctly. A has 15 people, B has 23 people, and C has 10 people, so the number of people in this class is easy to distinguish, that is, the area of C is removed. Namely: 15+23- 10=28.
Add:
Addition (usually indicated by the plus sign "+") is one of the four basic arithmetic operations, and the others are subtraction, multiplication and division. For example, in the picture below, * * * has a combination of three apples and two apples, and * * * counts as five apples. This observation is equivalent to the mathematical expression "3+2 = 5", that is, "3 plus 2 equals 5".
In addition to calculating fruits, you can also calculate other physical objects. Using system generalization, addition can also be defined on more abstract quantities, such as integers, rational numbers, real numbers and complex numbers, and other abstract objects, such as vectors and matrices.