Let's do it for you, 1: For a project, if it is contracted by Party A and Party B and completed in 12 / 5 days, it needs to pay 180000 yuan; if it is contracted by Party B and Party C and completed in 15 / 4 days, it needs to pay 150000 yuan; if it is contracted by Party A and Party C and completed in 20 / 7, it needs to pay 160000 yuan. Now the project is contracted by a single team. On the premise that the project can be completed in one week, which team has less contract cost? 2: When a shopping mall sells a commodity, its profit margin increases by 8 percentage points because the purchase price is 6.4% lower than the original price. Then the original profit margin of this commodity is... (Note: profit margin = (sales price purchase price) X100%. I can't understand the first floor product.) (just these two questions, 50 points.) 3: The number of integer solutions (x, y) of the equation x & sup2; + XY + 2Y & sup2; = 29 is () A.2 B.3 C.4 D. infinite

Let's do it for you, 1: For a project, if it is contracted by Party A and Party B and completed in 12 / 5 days, it needs to pay 180000 yuan; if it is contracted by Party B and Party C and completed in 15 / 4 days, it needs to pay 150000 yuan; if it is contracted by Party A and Party C and completed in 20 / 7, it needs to pay 160000 yuan. Now the project is contracted by a single team. On the premise that the project can be completed in one week, which team has less contract cost? 2: When a shopping mall sells a commodity, its profit margin increases by 8 percentage points because the purchase price is 6.4% lower than the original price. Then the original profit margin of this commodity is... (Note: profit margin = (sales price purchase price) X100%. I can't understand the first floor product.) (just these two questions, 50 points.) 3: The number of integer solutions (x, y) of the equation x & sup2; + XY + 2Y & sup2; = 29 is () A.2 B.3 C.4 D. infinite

1）
B
Suppose that the cost of a, B and C contracting for one day is a, B and C respectively
The projects that a, B and C can complete every day are respectively x, y and Z
Then a + B = 180000 * 5 / 12 = 75000
b+c=150000*4/15=40000
a+c=160000*7/20=56000
From the above three equations, a = 45500 / b = 29500 / C = 10500 can be solved
x+y=5/12
y+z=4/15
x+z=7/20
The solution is x = 1 / 4. Y = 1 / 6. Z = 1 / 10
That is, Party A, Party B and Party C can respectively complete 1 / 4, 1 / 6 and 1 / 10 of the project every day
It takes 4 days, 6 days and 10 days respectively for Party A, Party B and Party C to complete the project
The cost of a is 45500 * 4 = 182000, that of B is 29500 * 6 = 177000, and that of C is 10500 * 10 = 105000
Although C costs the least, it can't be completed in a week
So choose B
2）
Suppose the original purchase price is a yuan, then the new purchase price is (1-6.4%) a = 0.936a yuan. Suppose the original profit margin is x, then the new profit margin is (x + 8%). Since the selling price remains unchanged, the new profit margin is (x + 8%)
a（1+x）=0.936a（1+x+8%）
The solution: x = 0.17 = 17%
A: the original profit margin was 17%
3）C
∵ X & sup2; + XY + 2Y & sup2; = 29, then (x + 1 / 2Y) & sup2; = 29-7 / 4Y & sup2; ①
Since the equation has integer roots, the discriminant (x + 1 / 2Y) & sup2; ≥ 0.2 is a complete square number
By substituting ① into ②, 29-7 / 4Y & sup2; ≥ 0, that is - 7Y & sup2; + 116 ≥ 0, Y & sup2; ≤ 17 is obtained
The values of Y & sup2; are 0, 1, 4, 9 and 16,
The corresponding values of the discriminant (x + 1 / 2Y) & sup2; are 116109,88,53,4, respectively
Obviously, only when y & sup2; = 16, the discriminant 4 is a complete square, which meets the requirements
If y & sup2; = 16, then y = ± 4
When y = 4, the original equation is X & sup2; + 4x + 3 = 0, then x = - 3 or - 1
When y = - 4, the original equation is X & sup2; - 4x + 3 = 0, where x = 1 or 3
The integer solutions of the original equation are (- 3,4) or (- 1,4) or (1, - 4) or (3, - 4), totally 4 groups
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I can't see any more I went to sleep

Two mathematics problems of the first grade
1. Picture below
2. When x and y are of any value, the polynomial X & sup2; + Y & sup2; - 4x + 6y + 28 has a minimum value, which is requested
To process friends online and so on!
The first problem is; (x-1 power of a) & sup2; × x + 1 power of a △ 2x-1 power of A

2. The original formula = x-4x + 4 + y-6y + 9 + 15 = (X-2) square + (y + 3) square + 15. When x = 2, y = - 3, the minimum value of 15 is obtained

The second power of a + B = 10 AB + 10 [A-B]=

(a + b) twice = 100
A2 power + B2 power + 2Ab = 100
A2 power + B2 power = 100-2 * 10 = 80
A2 power + B2 power - 2Ab = 80-2ab
The second power of [A-B] is 80-20 = 60