7th grade summer math problems write equations process answers .

Round lose, 7 rounds win, 2Won't 3No.

If x people are arranged, there will be (10-x) people planted B.

There are 10 people in total).

Because each person can plant 3 acres of A vegetables, x people can plant 3x acres, and in the same way (10-x), people can plant 2 (10-x) acres of B vegetables.

Yes, because a kind of vegetables can earn 10,000 yuan per mu, 3x mu of vegetables can earn 3x * 10,000 yuan, and 2 (10-x) mu B vegetables can earn 2 (10-x) * 10,000 yuan, because the total income should not be less than 10,000 yuan.

then x 4

There are so many topics, one by one:

1. A=2, B=3, C=4, then 2A+B+C=11.

3. Let the number on the ten digit be a, then the hundred digit is a+4, the single digit is a+2, and the three-digit number can be expressed as 100 (a+4) + 10a+a+2, according to the three-digit number is 21 times the last two digits, column equation.

100 (a+4) + 10a + a + 2 = 21 (10a + a + 2), a = 3, and the three digits are 735.

4. If the leather clothing sold x pieces last year, the leather clothing sold 12,200-x pieces last year, the amount of leather clothing sold this year is x (1+6%), and the amount of leather clothing sold by B leather clothing is (12200-x) (1-5%), and the equation is listed.

x(1+6%)+12200-x)(1-5%)=12200+50, x=6000

Last year, 6,000 pieces of leather clothing were sold, and 6,200 pieces of leather clothing were sold.

5. The length of the train is x, which can be obtained according to the speed of the train.

290+x) 25=(128+x) 16, and the solution is x=160

6. Then the maximum value of m is not included in the minimum angle, the minimum angle is 180-m, and the maximum angle is 180-m+24, and the inequality can be listed.

180-m 180-(180-m)-(180-m+24) 180-m+24, the solution is 128 m 136, the minimum value of m is not included in the maximum angle, the minimum angle is 180-m-24, the maximum angle is 180-m, and the inequality can be listed.

180-m-24 180-(180-m-24)-(180-m) 180-m, the solution is 104 m 112, and in summary, the value range of m is 104 m 136.

Answer...

The first question should be 3

The second question should be calculated with a calculator, which is the content of the first year of high school, so it doesn't matter if you don't know.

Question 1: I really don't understand! It's scary to be in seventh grade now, it's a bit of a test of emotional intelligence! From the expression of the answer: more correct!

Let the amount of grass per cow per week be a, and the amount of grass per hectare per week is b, and the original amount of grass per hectare is c

12*4*a-3*4*b=3c

16a-4b=c

21*9*a-10*9*b=10c

189a-90b=10c

x*18*a-24*18*b=24c

3xa-72b=4cx=

+51)]

The other one is the same algorithm. Do the math for yourself.

1.Analysis: (1) The essence is to find the quadrants of x,y signs. A: x>0, and y<0 is in the fourth quadrant;

Another: x<0 and y>0, which is in the second quadrant.

Therefore, it is the second or fourth quadrant.

2) is the first and third quadrants.

2.(1) The point on the x-axis, the ordinate y=0, so m-1=0 knows the point on the m=1y-axis, and the abscissa x=0, so n+2=0 knows that n=-2(2)a,b,c,d four points in the line y=-xIf the four points cannot be obtained by observation in the line y=-x, let y=kx+b, try to bring the above four points in, and find k and b

In this problem, k=-1, b=0

1. (1) point p, one positive pair, so in the second or fourth quadrant, (2) point p is on the bisector of one or three quadrants, i.e., y=x

2. (1) The point ordinate of the x-axis is 0, so the abscissa of the point of the m=1y-axis is 0, so n=-2

2) The four points are all on a straight line, because their horizontal and vertical coordinates are all opposites, and therefore they are all on the straight line y=-x, i.e., the bisector of the two quadrants.

1 (1)xy must be one plus and one minus, obviously in two or four quadrants. (2) is a straight line that passes through one or three quadrants. 2(1)m=1 n=-2 (respectively so that m-1=0 n+2=0)(2) are above the straight line y=-x.