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According to the question stem, it can be set that A donated a book, B donated B book, C donated C book, D donated D book, it is easy to list the equation (b + c + d) 3 + a = 29, (a + c + d ) 3 + b = 23, (a + b + d ) 3 + c = 21, (a + b + c ) 3 + d = 19, the four equations deformation can be calculated a + b + c + d value, a total of 69 donated from the title can be seen that d donated the least, equation one subtracts equation four, and the value of a-d can be obtained

Answer: Solution: Suppose A donated copy A, B donated copy B, C donated copy C, and D donated copy D, it is easy to list the equation.

b+c+d) 3+a=29,a+c+d) 3+b=23,a+b+d) 3+c=21,a+b+c) 3+d=19, the above equation can be deformed as: b+c+d+3a=87, a+c+d+3b=69, a+b+d+3c=63, a+b+c+3d=57, add the four equations together, and get 6a+6b+6c+6d=276, so a total of donations: a+b+c+d=46 (this), From the question, it can be seen that Ding donated the least, equation 1 minus equation 4, to get a-d=15 (this), answer:

The four donated a total of 46 books, with a difference of 15 between the maximum number and the minimum number

The first is 48

A = 21 B = 12

C = 9 D = 6

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Mathematical logical thinking is very strong, don't be in a hurry to take notes in class, mainly understand, write down trivial or unintelligible, and do problems after class.

Which question do you ask? You name it, maybe I will.

First find the total area of the long reassurance, the length and width of the total reassuring area, and then find the area of the square, the length of the side The length of the side The total area of the square, and then the area of the rectangle How many square areas?

300 16 pcs.

A: 18 can be built. (This question does not conform to the actual situation, because if 18 are built, the gap between them is too small to allow people to walk back and forth, so the question is calculated like this, but if the mall is really built like this, it is unscientific).

2a-+c=0, tidy it up, grind to remove the brackets.

2a-+c=0

2a-+c=0

2a-b+a-2a-b+c=0

a-2b+c=0

c=2b-a

Substitute the letter travel base A and B.

8xy-2y -x +y =8xy-x -y

A: Get 8 out of 40 balls, buy 2 more, cost, 42 balls, 1050 yuan.

B: $20 per ball, $1,000.

C: 50 * 25 = 1250, 1250-12 * 20 = 1010 yuan.

B and C are both $20 each, and A is $1.

First, the conversion is carried out using the induction formula.

cos5 7=-cos( -5 7)=-cos2 7tan5 7=-tan( -5 7)=-tan2 7 f(x) is an even function.

f(-cos2 7) = f(cos2 7) f(-tan2 7) = f(tan2 7) and then compare the size of sin2 7, cos2 7 and tan2 7 4<2 7 2

sin2π/7>cos2π/7

tan2π/7=(sin2π/7)/(cos2π/7)>1>sin2π/7

f(x) is an increment function on [0,+.

c>a>b

The second-order partial derivative closed-door number of the multi-nuclear segment element composite function is used to solve the modified reputation.

Set Xiaoying's monthly water consumption to be xm3,5,x 5 from "if each household uses more than 5m3 per month, the excess part will be charged 2 yuan per cubic meter, and the water fee of Xiaoying's family in a month shall not be less than 15 yuan".

5, the solution: x, the tonnage is an integer, the minimum x is 9m3, so Xiaoying's water consumption this month is at least 9m3

176-4x10) 4-2 (176-4x10) x x 17/4 Solution: Let the number of people to Deqing be x and the number of people to Huaiji be y

Solve this system of equations to get:

The number of people who went to Deqing was 133, and the number of people who went to Huaiji was 67.

Solution: Set each shuttlecock x yuan, and each skipping rope y yuan column.

2 yuan per shuttlecock and 3 yuan per skipping rope.

The first question is not less than 10 yuan, assuming that the water fee is 10, then it is less than 10, which means that there must be exceedance, then the water consumption can be calculated at least 5+

The second question: April has 30 days, the first ten days produce an average of 4 per day, then the first ten days produced 40, there are 136 left unprocessed, after the improvement of technology, the speed is improved, three days ahead of schedule, that is, 17 days, at least 136 production, that is, an average of at least 136 a day, 17 = 8.

The third question: Shun'an Travel Agency organized 200 people to travel to Huaiji and Deqing, the number of people in Daodaoqing is twice the number of people in Huaiji, one less person, that is to say, after adding one person, the total number is three times that of Huaiji, that is, Huaiji has 201 3 = 67 people to Deqing has 200-67 = 133 people.

In the fourth question, the shuttlecock is set up to skip rope y yuan, and the two equations 5x+8y=34 3x+4y=18 are solved to get the shuttlecock 2 yuan to skip rope 3 yuan. Look).