For a mathematical problem, how to solve a practical problem with a quantitative relation?

Let puff be x years old, from the meaning of the title:

d+j=(x+s)+x+(x-p), and x=(d+j-s+p) 3;

Then set yertle to be Z years old, by the title:

d+j=z+（z+p）+（z+y）；The solution yields z=(d+j-p-y) 3;

Then the spot age is d+j-x-z (do the math yourself).

Quantity Relation: An equation that describes the relationship between certain quantities.

Commonly used quantity relations.

1. Unit price, quantity, total price.

2. Unit output quantity total output.

3. Speed time distance.

4. Ergonomics, time, and total work.

5. Addition + Addition and One Addition and Another Addition.

Minus Minus Difference Minus Difference Minus Difference Minus Difference Minus Difference.

Factor Factor Product One Factor Product Another Factor.

Dividend Divisor Quotient Divisor Dividend Quotient Dividend Quotient Dividend Quotient Divisor.

Division with remainder: The dividend quotient divisor + remainder.

If a number is divided by two numbers in a row, you can multiply the last two numbers first, and then remove the number with their product, and the result will not change. Example: 90 5 6 90 (5 6).

The relation is the "quantity of matter" between two or more substances.

Unit: Mo Kuan staring at the remorse)" relationship.

For example: addition, subtraction, multiplication and division.

Relationship between the parts:

1. Add the number of additions and. and one plus and the other plus.

2. The subtracted number is subtracted and the difference is subtracted. Subtracted Difference Subtracted. The difference subtracted by the subtracted number.

3. Factor Factor product. The product of one factor is another factor.

4. The dividend.

The divisor quotient. The dividend quotient is the divisor. The quotient divisor is the dividend.

Question 1: Set x common number f(x) rental fee.

x≤3f(x)=5

x＞3f(x)=5+

The second question is to set up the f(x) electricity fee between x passes.

x≤3f(x)=

x＞3f(x)=

The second question: ambiguity, each bell plus the yuan can be the original foundation, and then add the chaos of the Kai ruler to collect the yuan, consider the two questions, put them together, according to the department, each bell yuan, please ask Sun file.

(1) Use a fence with a total length of 60m to form a rectangular field, and find the relationship between the area of the rectangle s(m) and the length of one side x(m); The total length is 60m, one side is long x(m), the other side is long = (60-2x) 2=30-x, s = (30-x)x, one side is long x is variable, 30m is constant, 00(m s); (4) The bank stipulates that the annual interest rate of a five-year deposit is that a person deposits a principal of x yuan. then the relationship between the interest y (yuan) and the principal x (yuan) earned after five years.

y=, the deposited principal x (yuan) is a variable, the annual interest rate is constant, x> = 0 (yuan);