Math Problems About Inequalities Thanks!

It is most suitable for X years of use.

Average cost = total cost Number of years of use.

where sn is the sum of the first n terms of the series of a1=,d=.

sn=, you can then list the relationship between the average cost and x, and then find its minimum value mathematically.

Finally, we can see that the average cost = 10 x + x 10 + 1> = 2 + 1 = 3 if and only if 10 x = x 10 holds the equation, so x = 10

It is most suitable for use for up to 10 years.

The first two answers were perfect, it was 10 years, and the series of equal differences and the mean inequality were used.

Nine years!! Add the annual maintenance fee to the annual facility management fee!! n years.

There are x rooms, y students, and equations and inequalities are listed.

4x+19=y...1)

0 substitute (1) into (2) to get.

0<4x+19-6x+6<6

0<25-2x<6

Solution, x=10,11,12

y=59,63,67

So there are three possibilities:

10 rooms, 59 students.

11 rooms, 63 students.

12 rooms, 67 students.

Let an unknown number be calculated, that is, find a greatest common divisor

Room when 10-12 people are 59-67 won't ask me.

The answer on the 1st floor should be perfect, and if you are not satisfied, it is that there may be 1, 2, 3, 4, 5 people in a room 4 x 19 6 (x a).

A is substituted into the five numbers from 1 to 5 in turn, and the solution of the positive integer is the answer.

Room x, total number of people = 4x + 19

6＞ 6x - 4x +19） ＞16＞ 2x -19＞1

25 ＞ 2x＞ 20

x 10 -, x = 11 12 13 14 15 number = 4x + 19 ...

There are x number of rooms.

0＜4x+19-6x＜6

There are 7 rooms and 47 people.

There are 8 rooms and 51 people.

There are 9 rooms and 55 people.

Solution: (1) Set up the production of X sets of Type A refrigerators, then produce the sets of Type B refrigerators (100-X).

47500 (2800-2200)x+(3000-2600)(100-x) 48000

Solve 38 x 40

Therefore, the refrigerator factory has 3 schemes: the production of 38 A-type refrigerators and 62 B-type refrigerators; 39 A-type refrigerators and 61 B-type refrigerators were produced; 40 A-type refrigerators and 60 B-type refrigerators were produced.

2) The input is 2200x+2600(100-x)=-400x+260000

Therefore, when x = 40, that is, the production of 40 A-type refrigerators and 60 B-type refrigerators, the minimum investment is -400x+260000=-400*40+260000=244000 yuan.

Under this scheme, it is necessary to subsidize farmers (2800 * 40 + 3000 * 60) * 13% = 37960 yuan.

3) The profit is (2800-2200) * 40 + (3000-2600) * 60 = 48000 yuan.

Set up and buy A set of sports equipment, B set of experimental equipment, and C set of office supplies.

From the meaning of the title. a≤4…①

6000a+3000b+1800c=48000…②

Simplification yields 10a+5b+3c=80

It is easy to see that c must be a multiple of 5, and 01) when c = 5, 2a + b = 13, it is easy to see that b is an odd number and 13-4*2 b 13-2, so b = 5, 7, 9, 11

2) When c=10, 2a+b=10, it is easy to see that b is an even number and 10-4*2 b 10-2, so b=2,4,6,8

3) When c = 15, 2a + b = 7, it is easy to see that b is an odd number and 04) when c = 20, 2a + b = 4, it is easy to see that b is an even number and 0 In summary, b = 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, that is, there are 10 ways to buy experimental equipment.

.........This seems to be a quadratic function.

If the total sales revenue is y and the price is raised, the sales volume is (10,000 copies, then y = (2 + 10,000 yuan.)

Solution y== formula, y=

Because it is less than 0, (x-5)*2 is the minimum y maximum, so when x=5 is the y maximum.

So it should be $3.

Total revenue = (2+

First-order derivative: -2000x+10000=0, i.e. x=5

Therefore, when each magazine is 3 yuan, the sales revenue is the largest.

Multiplying the two sides of the equation by 2 to get 393 will definitely give a>2, but vice versa >2 will not necessarily get a>3.

Multiply by 2 above.

39 x + y 41 plus 2 y-x 4.

Get 41<2y<45 Same as dividing by 2 to get 2 Multiply by -1 on 2 y-x 4 to get -435< 2x<39 Same as dividing by 2 to get this problem, if you have learned linear programming.

Represents the area between two flat lines with a slope of -1.

2 y-x 4 represents the area between two parallel lines with a slope of 1.

The above four straight lines enclose a quadrilateral, and only the four vertices of the quadrilateral are required to obtain the required range.

The sum of the upper and lower formulas gives 41<2y<45 to get <

Subtract the two formulas, pay attention to the small subtraction and large subtraction to get 35 2x<39 to get <