The problem of quadratic equation of two variables 1. In order to improve the environment of the upper reaches of the Yellow River, a part of the pastures have been changed into forest farms. After the transformation, there are 162 hectares of forest farms and pastures, and the area of the pastures is 20% of the area of the forest farms. What is the area of the forest farms after returning farmland to forest? 2. The Xiaoming family saved 3000 yuan last year, and it is estimated that 5700 yuan will be saved this year. The income of this year is 15% higher than that of last year, and the expenditure is 10% lower than that of last year. What is the income and expenditure of last year? The first question is

The problem of quadratic equation of two variables 1. In order to improve the environment of the upper reaches of the Yellow River, a part of the pastures have been changed into forest farms. After the transformation, there are 162 hectares of forest farms and pastures, and the area of the pastures is 20% of the area of the forest farms. What is the area of the forest farms after returning farmland to forest? 2. The Xiaoming family saved 3000 yuan last year, and it is estimated that 5700 yuan will be saved this year. The income of this year is 15% higher than that of last year, and the expenditure is 10% lower than that of last year. What is the income and expenditure of last year? The first question is

1. Set the area of forest farm and pasture as X and y
x+y=162 (1)
y=0.2x (2)
Take (2) into (1) and get 1.2x = 162
The solution is x = 135
So the forest farm area is 135 hectares
2. Let the income and expenditure of last year be x and y
x-y=3000
1.15x-0.9y=5700
Using the method of addition and subtraction, we can get x = 12000, y = 9000
So last year's income and expenditure were 12000 yuan and 9000 yuan

There is a certain amount of alcohol in each of the three containers a, B and C. If you first pour 13% of the alcohol in container a into container B, then pour 13% of the alcohol in container B into container C, and finally pour 13% of the alcohol in container C into container a, then there are 13 kilogram of alcohol in each of the three containers?

According to the meaning of the title, we can know that there is a total of alcohol in the three containers: 13 × 3 = 1 (kg). Suppose that the original alcohol in container a is x kg, the original alcohol in container B is y kg, and the original alcohol in container C is 1-x-y kg. From the meaning of the title, we can get: (y + 13X) × (1-13) = 13 [(1-x-y + 13 × (y + 13X)] × 13 + (1-13) x = 13, which is sorted out as: 2x + 6y = 310x-6y = 0; solving the equations, we can get: x = 14y = 512 ．