The calculation problem of the binary system of equations in the first year of junior high school

I'm solving problems, not looking for problems.

Do you want me to help you solve the problem or help you find practice?

17x+8y=36 x=2 y=¼18x-18y=18 x=2 y=1

y-3x=0 x=1 y=3

x=2y x=2 y=1

In fact, you don't have to do the questions, just be careful.

It's addition and subtraction, it's substitution.

2x+9y=81

3x+y=12 [substitution] answer.

x=9 y=7

2x+5y=2

20x+5y=20 [addition and subtraction] A.

Table; x=1 y=5

79x-76y=-4388

26x-y=832 [substitution] Answer: x=32 y=917x+5y=54

3x+4y=38 [addition and subtraction] answer; x= 2 y= 8

You can refer to the example questions in your textbook, and just change the numbers in it.

Plan 1: Produce up to 4t milk tablets, and sell the rest of the fresh milk directly, then its profit is: 4 * 2000 + (9-4) * 500 = 10500 (yuan) Plan 2:

If 1 day of milk tablets is produced, the remaining 8t of yogurt can be produced for more than two days, which does not meet the conditions of exactly 4 days to be completed, therefore.

Not this method.

If the milk flakes are produced, the rest of the yogurt is produced exactly in 4 days, so it is produced in this way.

then the profit is: yuan).

12000-10500=1500 (yuan).

Therefore, every two plans can produce milk tablets per day, and the production of yogurt per day can get an extra profit of 1,500 yuan.

Plan 1: 4 tons of milk tablets are made, and the remaining 5 tons are sold as fresh milk, profit: 4 * 2000 + 5 * 500 = 10500 yuan;

Scheme 2: Set up x days of processing milk tablets, and the equation can be listed: x+3(4-x)=9, you can know x=, so a total of tons of milk tablets, tons of yogurt, profit: yuan, so the second scheme is the most profitable!

I was tired of doing it when I was in junior high school, but I didn't want to play because of the process. Calculate it yourself, little sister, this kind of application problem is too simple, just sort it out yourself.

You don't have to use a binary equation.

Assumptions can also be used.

Hehe, so modest, I'll see!

Well, it's only 1t, right?

1. Let the male student have x people and the female student have y people according to the question to list the equation to obtain:

x-4）+（y+3）/2=40

2（x-4）+（y+3）/2=68

Solving the system of equations yields x=32, y=21

2. The merchant purchased 6 mobile phones of type B, X part of type A mobile phone, and part Y part of type C mobile phone, and the equation was obtained according to the meaning of the question.

x+6+y=40

1800x+6 600+1200y=60000 Solve the equation to get x=26 y=8

The merchant purchased 7 mobile phones of type B, X mobile phones of type A, and part y of mobile phones of type C, and the equations were obtained according to the inscription.

x+7+y=40

1800x+7 600+1200y=60000 Solve the equation to get x=27 y=6

The merchant purchased 8 mobile phones of type B, X part of type A mobile phone, and part Y part of type C mobile phone, and the equation was obtained according to the question.

x+8+y=40

1800x+8 600+1200y=60000 Solve the equation to get x=28 y=4

Just answer them separately.

x for males and y for females, 2*(x-4)+(y+3) 2=68

x-4)+(y+3)/2=40

x=32，y=21

A is x, B is y, and C is 40-x-y

1800x+600y+1200(40-x-y)=60000 because 6<=y<=8

Simplification x-y = 20

So there are 3 cases 26, 6, 8, 27, 7, 6, 28, 8, 4