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The seventh grade mathematics unary linear equation problem.
1, when the water velocity is x km/, the equation is obtained according to the meaning of the question.

7×( 16+x)=9×( 16-x)

X = 2km/h is obtained from the solution.

The water flow speed is 2 km/h.

2. If the number of questions answered incorrectly is x, the number of unanswered questions is 2x, and the number of questions answered correctly is (25-3x).

Get the equation according to the meaning of the question

4×(25-3x)-2×x=86

For solution, X= 1, for 25-3x, x = 22.

22 correct answers

3. Let the number in the tenth place be X, then the number in the hundredth place is x- 1, and the number in the unit place is 3x+2.

Get the equation according to the meaning of the question

x+x- 1+3x+2 = 1 1

X=2, so the percentile is 2- 1= 1, and the unit digit is 3×2+2=8.

So this three-digit number is 128.

4. If the length is x cm and the width is (24-x) cm, the equation is obtained according to the meaning of the question.

[x-(24-x)]x = 0.4

X= 15, so the width is 24- 15=9.

Design length 15cm, width 9cm.

5、3(3x+7)-2(2x- 1)=8

X=-3 is the solution.

6.①y 1=y2 means 1/2x- 1=2/3x-3. Just solve this equation. I don't understand. Is x on the denominator?

②y 1 and y2 are opposite numbers, that is, y 1=-y2, that is, 1/2x- 1=-2/3x+3. I still don't understand whether x is on the denominator.

Multiple choice

Question 1 answer: 3, -8

The answer to the second question: 2

The answer to the third question: 80, 82, 84

The answer to the fourth question: 3x+ 14-x-5= 19, which is 2x- 10=0 after finishing.

The answer to the fifth question: x÷6-(x-2×4)÷4= 1/4, and it will be x-2 1=0 after completion.

Typing dizzy! The above answers are for reference only! 0 points, poor!