Uncle Li bought the same number of a and B rabbits a year ago. At present, the number of these two kinds of rabbits he raised is still the same, and the number of a kind of rabbits has increased by 20, while that of B kind of rabbits has decreased by 10. (1) how many kinds of rabbits did Uncle Li buy a year ago? (2) At present, Mr. Li is ready to sell 30 breeding rabbits. It is known that he can make a profit of 15 yuan per rabbit of type A and 6 yuan per rabbit of type B. if he wants to sell less rabbits of type A than rabbits of type B, and the total profit is not less than 280 yuan, what kinds of rabbit selling plans does he have? Which scheme is the most profitable? Ask for the maximum profit

(1) Suppose Mr. Li bought x rabbits of a and B a year ago, then he got x + 20 = 2x-10 and x = 30, that is, he bought 60 breeding rabbits a year ago. (2) suppose Mr. Li sold y rabbits of a and 30-y rabbits of B, then he got Y & lt; 30-y ① 15y + (30-y) × 6 ≥ 280, and then he got Y & lt; 15

On linear inequality of one variable
If no one divides apples into four, there will be nine left. If everyone divides apples into six, then the last child will get less than three apples. How many apples and how many children

There are x children
Then Apple has 4x + 9
According to the meaning of the title: 0 ≤ 4x + 9-6 (x-1) < 3
The solution is 15 / 2 ≥ x > 6
Because x is an integer
Then x = 7, Apple has 4 * 7 + 9 = 37

Mathematical problems in the first grade of junior high school
The practical problem is related to the linear inequality of one variable
1. The purchase price of apple is 1.5 yuan per kilogram, and it is estimated that 5% of the apples are in normal loss. How much can the seller fix the price at least to avoid losing money?
2. It takes 10 hours for a ship to travel from a place upstream to B place downstream at an average speed, and less than 12 hours for a ship to return to a place from B place at an average speed. The water velocity of this section of the river is 3 km / h, and the static water velocity V of the ship to and fro is constant. What conditions does V meet?
If the answer is correct or good, a reward will be offered

(1) Let the price be at least X Yuan,
Then x (1-5%) ≥ 1.5
The solution is x ≥ 30 / 19
（2）S／（v＋3）=10
S/（V-3）≤12
The solution is v ≥ 33

Given a + B = 5, ab = 3, find ① a + B; ② A-B; ③ A-B; ④ a of B + B of a; ⑤ a-Ab + B;

① (a-b) \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\it's not easy

Given that two of the equations x2-3x + 1 = 0 are X1 and X2, then: X12 + X22= ，1x1+1x2= ．

From the meaning of the title, X1 + x2 = − Ba = 3, x1x2 = CA = 1, X12 + X22 = (x1 + x2) 2-2x1x2 = 9-2 = 7, 1x1 + 1x2 = X1 + x2x1x2 = 3, so fill in 7; 3

Solution equation ((13x-x ^ 2) / (x + 1)) (x + (13-x) / (x + 1)) = 42

(X(13-X)(X+(13-X)))/(X+1)=42
The denominator is x ^ 2 (13-x) + (13-x) X
The molecule is (x + 1)
Re score mother x (13-x) (x + 1)
(x + 1) x = 42
We get x = 6

The continuous natural numbers 1, 2, 3 The order of n (n ≥ 3) is disordered and rearranged into A1, A2, A3 If (A1-1) (A2-2) (A3-3) If (an-n) is an odd number, then ()
A. It must be even B. it must be odd C. It may be odd or even D. It must be 2m-1 (M is odd)

If n is an even number, the number of even numbers is equal to the number of odd numbers in the sequence of 1 ~ n, and (A1-1) (A2-2) (A3-3) If (an-n) is odd, every term must be odd. Because the odd and even numbers in A1 ~ ～ an are equal, it is possible to find a sequence 1 ~ ～ n such that (A1-1) (A2-2) (A3-3) (an-n) every term is an odd number. If n is an odd number, the number of even numbers in the sequence of 1-N is one less than that of odd numbers. To ensure that (A1-1) (A2-2) (A3-3) If (an-n) is an odd number, every item must be an odd number. Because there is one more odd number than even number in A1 ~ an, it must be in (A1-1) (A2-2) (A3-3) There is an even number in (an-n), so (A1-1) (A2-2) (A3-3) (an-n) must be even, so n must be even

X ^ 2-14x-6 = 0 solution

x^2-14x-6=0
x²-14x=6
x²-14x+49=6+49
(x-7)²=55
x-7=±√55
x=7±√55
x1=7+√55,x2=7-√55

(x1-x2 + 4x3-2x4 = 0; x1-x2-x3 + 2x4 = 0; 3x1 + x2 + 7x3-2x4 = 0; x1-3x2-12x3 + 6x4 = 0) I don't know which step is wrong, please give me an answer

Because the rank of coefficient matrix is equal to 4 and the number of unknowns
So this system of homogeneous linear equations has only zero solution

If x2-2 (M-3) x + 25 is a complete square, what is the value of M?

∵ x2-2 (M-3) x + 25 is a complete square, and the solution is m = 8 or - 2

On linear inequality of one variable If no one divides apples into four, there will be nine left. If everyone divides apples into six, then the last child will get less than three apples. How many apples and how many children