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b This is a Newton cow grazing problem.

Also consider the growth rate of the grass.

Let 1 sheep eat grass x every day, that 1 cow eats grass 4x every day, and then set the grass to grow y every day, and there is grass m

List the two equations:

m+20y=16×4x×20

m+12y=80×x×12

Subtract the two formulas to get 8y=320x, simplified to y=40x, m=480x, so 10 cows and 60 sheep eat this piece of grass together, how many days can they eat?

According to the conditional column, you can eat a day.

480x+a 40x=(40x+60x) a solution a=8

So the answer is 8 days.

Suppose each cow eats one serving of grass per day

80 4 = 20 (head) 604 = 15 (head).

Newly added grass every day:

Original grass: 1620-1020=120

10 cows eat the new grass that is added every day, and 15 cows (60 sheep) eat the original grass:

120 15 = 8 (days).

If grass growth is not taken into account, if a sheep eats grass every day as a, then 1 cow is 4a. It was found that 16 cows ate 20 days to get 16 * 20 * 4a = 1280a, 80 sheep ate 12 days to get 80 * 12 * a = 960a, the same grass is different, so the growth of grass should be considered.

If the growth rate of forage grass is y, then 1280a-20y=960a-12y, y=40a, and the original forage grass is 1280a-20y=480a

Set the problem to be eaten in x days, 480a+40a*x=(10*4a+60*a)*x, x=8 choose b

Answer: A Suppose each sheep eats A per day, i.e., the cow eats 4a per cow per day

Therefore, 80*12*a, that is, the total amount of forage divided by 10*4a+60a, that is, the sky is obtained, so it is to choose a

Xinglong electrical appliance store sales of the same model of the machine, according to the purchase price of 20% of the sales, sold out of this batch of electrical appliances can make a profit of 6000 yuan, because of the 10 of the machine some damage, the 10 machine according to the sales price of the sale, so the total profit is only expected to be 96%, how many of these machines?

6000*(1-96%) (10-9)--The unit price is set to the quantity x the quantity to be solved: 150

This batch of *** machines has x unit price: (6000 20%) x=30000 x [6000*(1-96%)] 10=(30000 x)*(1+20%-90%)=9000 x 24=9000 x x=375 There are 375 *** machines in this batch.

Price: Unit = 6000 * (yuan.)

Profit per unit = 240 yuan.

Total number = 6000 40 = 150 units.

25 units The purchase price is 1200 yuan per unit

We have set a total of x units, and the purchase price of each unit is Y yuan. Then: (y+20%y) is the sales price, so (120%y*x) is the expected normal sales income, and the purchase price is xy.

So we can get Equation 1（x*120%y）-x*y=6000;

According to the question, we can also know that the good *** sales income is: 120%y*(x-10); The sales income of the damaged *** is: 120%y*90%*10; So we can get Equation 2 again

120%y(x-10)+120%y*90%*10=120%y*x*96%;

Summarizing the above two equations, we can get x=25 units; y=1200 yuan.

According to the title.

Team B did it alone for 2 days and was able to complete:

A and B cooperation completed:

A and B cooperate, completed every day:

A and B cooperated:

3 4 7 24 = 18 7 days.

Comprehensive formula: 1-1 8 2) (1 6+1 8) = 18 7Answer: The two have worked together for 18 7 (2 and 4 7) days.

Team B did it alone for 2 days and was able to complete:

A and B cooperation completed:

A and B cooperate, completed every day:

A and B cooperated:

3 4 7 24 = 18 7 days.

Comprehensive formula: 1-1 8 2) (1 6+1 8) = 18 7Answer: The two have worked together for 18 7 (2 and 4 7) days.

Set up the cooperation to be completed in x days.

1/6+1/8）x+2*1/8=1

Solution x = 18 7

Team A's efficiency: 1 6

Team B Efficiency: 1 8

Set up the cooperation to be completed in x days.

1/6+1/8）x+2*1/8=1

Solution x = 18 7