If you don t know how to solve the application problem, you won t know how to do it, and you need to

If the rent is increased by x (x is greater than or equal to 0) times, the daily room rental income is the highest, and the room rent is set to y. After the increase, the rent** is (20+2x), and the number of rooms rented is (300-10x), and the equation is:

y=(20+2x)(300-10x)

20 (-x squared + 20x + 300).

Then find the maximum value according to the equation, when x=-2a b, i.e., x=10, y=8000

When the rent is increased by 10 times to 200 yuan, the maximum room rent per day is 8,000 yuan.

Solution: When the rent of the hotel is increased by x two yuan, the daily room rental income is the highest.

Room rental income per day = number of rooms rented per day Rent per room.

i.e. room rental income per day = (300-10x) (20 2x) 20 x-10 8000

So when x 10, the daily room rental income is the highest, and the highest income is 8000 yuan.

Set the rent to be increased x times.

300-10x)*(20+2x) = 20 x-10 8000 When x 10, the daily room rental income is the highest, and the maximum income is 8000 yuan.

Suppose: Each house increases by 2x, then each house** is 20+2x, and the total income obtained is y, so there is: y=(20+2x)* 300-10x)y=-20(x2-20x-300).

y=-20[（x-10）2-400]

When x=10, get a maximum income of 8000

Note: x2 is the square of x, and (x-10)2 is the square of (x-10).

According to the question, another 180 kg was shipped back, and the new pineapple shipped back was exactly 25% of the pineapple before selling, which means that 25% of the total pineapple before sale was 180 kg, so the total amount of pineapple before sale was.

180 25% = 180 4 = 720 kg.

The existing pineapples should be the original total minus the sold, plus the new shipments.

612 (kg).

Before selling: 180 25% = 720 kg.

Sell 40% remainder: 720 (1-40%) = 432 kg.

Existing: 432 + 180 = 612 kg.

The speed of the butterfly.

The speed of the bees.

That is, the bees travel kilometers in one hour.

I'm using a quadratic equation, so I don't know if there's an easier way.

Let the original student be x, 840 x-15=(840+150) (x+3), 840 x-15=990 (x+3), multiplied by x(x+3), 840(x+3)-15x(x+3)=990x, 840x+2520-15x-45x=990x, 15x +195x-2520=0, x=8 (x=-21 rounded).

It turned out that there were 8 people.

Solution: It will take X days for the rest of the two teams A and B to cooperate.

According to the title, we get 1-(1 20 8+1 30 3)=(1 20+1 30)x

Solution x = A: The rest of the two teams A and B still need to be debated fiercely.

Because it takes 20 days for A to complete all the work, the work efficiency of A is one-twentieth of the dust and the height of the ruler.

In the same way, the ergonomic efficiency of B is one-thirtieth.

Ergonomics Working time = total amount of work.

17 minutes.

Suppose a1 b2 c5 d10

A B together, it took 2 minutes, A came back, let C D go together, a total of 11 minutes, B came back and picked up A took 4 minutes. 2 + 11 + 4 = 17 minutes.

Add up the two newspapers, and you're the whole class:

More than the class: 19 12-1 = 7 12

These 7 12 are determined by both:

48 7 12 = 28 people.

Comprehensive formula: (5 6 + 3 4-1) 48 = 28 people.

It's hard to describe without x and y.

1. Let the read be x pages, then.

What I haven't read is: 5x 7 2 5

then there is x+5x 7 2 5=153

The solution is x=119

2. In the end, there are 60 grams left, then the third time before pouring is 180 + 60 = 240 grams, and the second time to the first remaining 5 9, then 240 grams is the first remaining 4 9, so the first time the remaining is 240 (4 9) = 540, from the title you can know that there is: (540-40) (2 3) = 7503, class A has x people, then class B has 84-x, x 5 8 + (84-x) 3 4 = 58

The solution yields x=40

There are 44 people in Class B.

4. The speed of the express train is 1 5 per hour, the speed of the slow train is 1 8 per hour, and the express train departs for two hours, then the remaining distance is 3 5 The whole journey, and the time t is set to meet the two cars.

1/5+1/8）×t=3/5

The solution yields t=24 13

At this time, the distance between the two cars is 84 kilometers, and the length of the whole journey is y kilometers, then there is y 5 2 + (y 5-y 8) 24 13 = 84 2 to solve y=312 kilometers.

5. After setting the burn for x hours, if the requirements of the topic are met, there is.

1-1/4×x=2×（1-1/3×x）

The solution gives x=12 5=

That's 2 hours and 24 minutes.

Then it needs to be lit at the same time at 1:36 p.m.

6. Let the remaining is x kilometers, then x=(900+x) 3 4-300

Solution x=1500

So the overall length is 1500 + 900 = 2400

7. Set the original x book, then.

The first group has (x-1) 1 7+1

The second group has [(x-1) 6 7-2] 1 7+2 and finally the groups are equal, then there is.

x-1) 1 7+1 = [(x-1) 6 7-2] 1 7+2 solves x=36, then each group is 6 books.

8. Let there be x people reading books, of which girls are x 4 19, and after 2 girls come, x 4 19 + 2 = (x + 2) 9 19

The solution yields x=4

But there must be a problem with the question design, because the number of girls cannot be a decimal point. You then check the data of the question.

9. It is equal to 1988 1 2 2 3 3 4 ......1987 1988 It can be seen that the denominator of 1 2 is reduced to the numerator of 2 3, and then it is reduced one by one, leaving only 1988 1 1988 = 1

Solution: Because 5 or 6 people have subscribed to the language newspaper.

Therefore, there are 48 * 5 6 = 40 (people) who subscribe to the language newspaper, because 3 4 people subscribe to the math newspaper.

Therefore, there are 48 * 3 4 = 36 (people) who order the math report, because 40 + 36 = 76 (people), which is greater than 48 people.

So both readings are ordered 76-48=28 (people).

The bus traveled 60 km).

The truck went 250-90 = 160 (km).

Truck speed 160 2 = 80 km h.

A: Trucks travel 80 kilometers per hour.

Trucks are set to travel x kilometers per hour.

x = 260 3km is approximately equal to.

No, you can ask me again.

Hope it helps.