The formulas of "before the word" and "after the word" are "before the word", adding more and subtracting less, and subtracting the middle word. The formula of comparing the front word with the middle word is the formula of mathematics in the first grade of primary school. In order to facilitate the memory of first-year students, there are reminders to compare words. Formula is a Chinese vocabulary, and later it refers to sentences that are easy to remember according to the main points of things. Comparison is a division formula composed of the former item and the latter item, but the division symbol is changed to the comparison symbol, which is another expression of division. But the division formula represents an operation, and the ratio represents the relationship between two numbers, similar to the fractional line of a fraction. For example, if you divide 6 by 4, write 6 divided by 4 in the form of ratio.