The calculation formula of the total number of people having meals is as follows: number of people having meals = number of people having breakfast × breakfast meal ratio+number of people having Chinese food × Chinese food meal ratio+number of people having dinner × dinner meal ratio.

These are four simple arithmetic application problems, which are the learning contents of primary school mathematics.

Four operations refer to four operations: addition, subtraction, multiplication and division. Four operations are the important content of primary school mathematics and the basis of learning other related knowledge. Multiplication is a simple operation of addition and division is a simple operation of subtraction. Subtraction is the inverse of addition and division is the inverse of multiplication.