I asked someone to help me do these math problems in the first year of junior high school, and I sta

A person exhales 38 grams of carbon dioxide in an hour, and 10,000 people exhale 38 * 24 * 10,000 grams a day, which is a ton. And because one hectare of forest can absorb about 1 ton of carbon dioxide per day, that horse absorbs tons of carbon dioxide with hectares of forest. And because the result retains 2 significant digits, the answer is hectares (the equation is 1*38*24*10000 1000000).

Is this really a math problem in the first year of junior high school?

10,000 people a day: 38 * 24 * 10,000 = 9,120,000 (g) = tons. hectares).

38x24=912 grams for one person a day.

10,000 people 9,120,000 grams = 9,120 kilograms = tons.

So hectares of woods are needed.

This is simple, when x=2, 8x 3+2x+1=6, so 8x 3+2x=5, so, when x=-2, -8x 3-2x+1=-5+1=-4

Substituting x=2 into ax to the 3rd power + bx+1 gives 8a+2b+1=6, i.e., 8a+2b=5, so -8-2b=-5

Substituting x= -2 to the 3rd power of ax +bx+1 gives -8-2b+1 and substituting -8-2b=-5 as a whole to -8-2b+1 gives -8-2b+1=-4

That is, to the power of ax to the 3rd power +bx+1=-4

1. Let the cow eat grass every week for x, the forage grows y every week, the original forage has the quantity of a, you can list the equations, 10 * 20x + a + 10y = 0, 24 * 6x + a + 6y = 0 (one is to eat, one is to grow, and finally 0), solve the equation to get x = -a 60, y = 7a 30 (eat is negative, the growth is positive, and vice versa), and then set 18 cows can eat m weeks, and substitute the formula to get 18 * m * (-a 60) + a + m * 7a 30 =0, in this equation, we can reduce a, solve the equation, m=15

2. This question is actually the same type as the first question, you need to set a constant, the constant in the above question is the original amount of pasture, and the constant of this question is the water that has leaked in, the specific solution process will not be said, the result of the calculation is, people can not be decimals, so it is 24 people.

3. Similar to the previous two questions, but slightly different, the specific solution: let the total amount of wine be a, the daily alcohol leakage is x, and the amount of alcohol per person per day is y, at this time, we can list two equations, which are a + 12 * 4y + 4x = 0, a + 9 * 5y + 5x = 0, at this time, there is no need to solve the equation, and the unknown number y can be eliminated by the elimination method, and x=a 20 can be solved, that is, the amount of alcohol leakage per day is one-twentieth of the total amount of wine.

These three questions have two things in common that need to be noted, the first is that there is a positive and negative relationship, and the second is to add a constant.

The train is seen as stationary, the tunnel and the lights are seen as moving, the tunnel entrance covers the train to the end of the tunnel in 20 seconds, 300 meters long, the lights are stationary relative to the tunnel, illuminates the train for 10 seconds, the train length is set to x, there are 300 20=x 10

Let the length of the train be x, and there it is.

300+x）/20=x/10

x = 300 meters.

3.Because "it is known that apples are 25 yuan per box, pears are 20 yuan per box, and grapes are 16 yuan per box." The total amount of money is 426 yuan, and the unit digit is "6", indicating that the number of boxes of grapes is "6, 10, 16 or 20 boxes", and only "16" matches the theme.

16 16 = 256 yuan, 426 256 = 170 yuan, and the number of boxes of apples may be "2 or 6 cases". If apples are 2 boxes, then pears are (170 25 2) 20 = 6 boxes. Three kinds of fruit are exactly 16 2 6 = 24 boxes.

If the apples are 6 boxes, then the pears are (170 25 6) 20 = 1 box, which does not fit the topic. So the unit bought 2 boxes of apples.

Let the amount of water flowing into the pond per hour be x, the amount of water pumped by 1 type A pump per hour is y, and the original water volume of the pond is a:

x+a=y1/3)x+a=(1/3)*2y

Beg? *x+a=3*？*y?

From the first two formulas, it can be deduced: a=y-x

y=2x so the third equation can be made as: (?) 1）x=?*6x?+1=6?

1 5 1 5 hours is 12 minutes 6The solution set from the inequality (2m-n)x+3m-4n 0 is x 4 9, and (2m-n)4 9 = 4n-3m and 2m-n<0, i.e., 8m-4n=36n-27m

35m=40n

n=7/8m

and 2m-n<0

Therefore, 2m<7 8m is m<0

Substituting n=7 8m into the inequality yields.

m-4*(7/8m)]x+2m-3*(7/8m)>0-5/2mx>5/8m

4mx>0

Because m<0 is -4m>0

So x>0

That is, the solution set of the inequality (m-4n) x+2m-3n>0 is Note: the above method is done according to the inequality (m-4n) x+2m-3n>0, if it is (m-4n)x+2m-3n<0, then the solution set is.

1. The addition of the two formulas can have mx+3x=10

That is, x*(m+3)=10, 10=1*10=2*5, when x is negative, m+3 is negative, so we are also negative, and if the conditions are not met, so x>0

When x=1, m=7

When x=2, m=2

When x = 5 and 10, m is negative.

So m=2 or 7

2. The equation 3kx+2y=6k-3 for x and y has the same solution for any value of k.

There are infinite solutions to the equation (3x-6) k+2y+3=0 for k, so 3x-6=0 and 2y+3=0

x=2，y=-3/23、

⒈ mx+2y=10 3x-2y=0；then (m+3)x=10;

m is a positive integer, i.e., (m+3)>3, then x>0;

It can be taken as m+3=5, x=2 or m+3=10, x=1

y=3 2x, m=2

3kx+2y=6k-3, that is, (3x-6)k+2y+3=0

Any value of k has the same solution, i.e., 3x-6=0;2y+3=0, then the solution x=2, y=-3 2

Set x boxes for apples, y boxes for pears, and boxes for grapes (24-x-y); x,y are integers.

The equation is: 25x+20y+16(24-x-y)=426;Simplification 9x+4y=42, for x, x can only take 2, then y=6, z=16

The unit purchased 2 boxes of apples.

Set up x 50 points and Y 20 points; x,y are integers.

50x+2 20y=350, i.e. 5x+4y=35;

Only x=3, y=5;3 should be added

Let the original water depth be a, the water inlet velocity is x, the pumping speed is y, and the time required is t;

then 60x+a=60y, 20x+a=2 20y, subtract, y=2x, substitution, a=60x;

and tx+a=3 ty, substitute y=2x, a=60x, and get t=12, that is, it takes 12 minutes.

solution(2m-n)x+3m-4n<0,x>(4n-3m) (2m-n);

Then (4n-3m) (2m-n)=4 9, simplified to m=8n 7, substituted by inequality (m-4n)x+2m-3n>0, that is, (8n 7-4n) x+16n 7-3n>0, and n<0, then reduce n, get x>-1 4

1. Add the two formulas to get (3+m)x=10

Arrays where two integers are multiplied by 10 are: 1 and 5, -1 and -10, -2 and -5

Since m is a positive integer, there is m>0,3+m>3, so we can know that 3+m=5, m=2 Second, we can know that the left and right sides are equal to k as unknowns, and there are: 3x=6, x=2;2y=-3, y=three,

-- It's a lot -- but it's all simple, leave it downstairs!

Or I'll do it-

Question 1: The preceding formula plus the posterior formula=> (m+3)x=10 , since m is a positive integer, and x is also, we can know that m=2, or m=7

Question 2: Assuming k is an unknown number, then the original formula is: (3x-6)k+2y+3=0, then =>x=2, y=

Question 3: From the end of the phone bill 6, it can be seen that the grapes are either 1 box, or 6 boxes, or 11 boxes, or 16 boxes or 21 boxes, and then suppose it is 1 box, then let the other 2 be x,y column equations, x+y=23, 25x+20y=410, no solution, then 6 boxes, x+y=18, 25x+20y=330, no solution, in the same way, when 11 boxes, no solution, 16 boxes, x=2, y=6, 21 boxes, no solution.

Question 4: If 20 points buy x cards and 50 points buy y cards, then 2x+x+y=18, 20x+20x+50y=350,=> y=3

Question 5: Let the water flow rate be x per hour, the pumping machine will pump y flow per hour, and there is a amount of water in the yuan pool.

a+x=y, a+1 3x=2*1 3y =>y=2a, x=a, then when using 3 units, a+a*t=3*2a*t =>t=12 minutes.

Question 6: The original formula is solved as: x>(4n-3m) (2m-n) and 2m-n<0 i.e. 4n-3m) (2m-n)=4 9 =>m=8 7n and m,n<0, in , bring in the following equation: x>(3n-2m) (m-4n)=, i.e. x>

1. x=2 y=3 m=2

2. x=2 y=

3. 2 boxes of apples.

Fourth, 3 pieces. 5. 12 minutes.

2.A vendor counts large eggs for 3 jiao and 6 points each. Small eggs sold some eggs for 2 jiao 8 points each, earning a total of 1Solution: If there are x female employees, then there are 1240-x male employees, according to the title: 3 8x=2

1 First, the two formulas are added to give (m+3) x = 10

Because x is an integer when x=1 m=7

m=3 when x=2

m=5 m is not an integer.

Because y is also an integer, and when the above two cases are substituted into 3x-2y=0x=1, y= is not true, so the first case is rounded.

m=22 shifts.

x=2 y=

1、m=2

2、x=2，y=

I don't have time to count the rest for the time being.