The difference between a and B is 9.9. If the decimal point of a is moved one place to the left, it is equal to B. what is the number a and B?

The difference between a and B is 9.9. If the decimal point of a is moved one place to the left, it is equal to B. what is the number a and B?

If the decimal point of a is moved one place to the left, it is equal to B, and a is 10 times of B
B is 9.9 ÷ (10-1) = 1.1
1 × 10 = 11

Given x ^ 2 + y ^ 2-2x-4y-4 = 0, find the value range of X + y

x^2+y^2-2x-4y-4=0
(x-1)^2+(y-2)^2=9
Let x = 1 + 3cosa, y = 2 + 3sina
x+y=3(1+cosa+sina)
=3+3(sina+cosa)
=3+3√2sin(a+π/4)
Because - 1 ≤ sin (a + π / 4) ≤ 1
So 3-3 √ 2 ≤ x + y ≤ 3 + 3 √ 2

There are three classes planting trees in the sixth grade of experimental primary school. The number of trees planted in the first class accounts for 1 / 4 of the total number of the three classes. The ratio of the number of trees planted in the second class and the third class is 3:4. The number of trees planted in the second class is higher than that in the third class
I know the formula. Why do I do it like this
Use it tomorrow!
24 × 3 = 72 (trees) 2 classes (why do you do this)
24 × 4 = 96 (trees) 3 classes (why do you do this)
(72 + 96) △ 3 / 4 = 224 (trees) (why do you do this)
224-72-96 = 56 (trees) class 1 (why do you do this)

Because the ratio of class 2 and class 3 is 3:4, we can regard class 2 as 3, class 3 as 4, if there is a difference of 1, there will be a difference of 24, so that one is 24

LX + 1 △ x-1l < 1, solve inequality

It can be divided into two formulas: ① (x + 1 ／ x-1) ＜ 1; ② - (x + 1 ／ x-1) ＜ 1

On the eve of new year's day, all shopping malls have unified pricing, but adopt different promotion policies
Century Lianhua: 15% off
Agribusiness Supermarket: buy four get one free
Jiajia Supermarket: 10% discount and 20 yuan return fare
Suguo Supermarket: 16 yuan for every 100 yuan
Now Duoduo wants to buy the following items. Which one is the best? How much is it?
(1) Buy a 3000 yuan refrigerator
(2) Buy a notebook with a unit price of 30 yuan and 10 yuan
It's a formula!

It depends on how much you spend. You can spend X Yuan
The following formula is the actual value you get for spending X Yuan
Century Lianhua: (1-0.85) x + X
Agriculture, industry and Commerce: (1-0.75) x + X (for commodities with quantity greater than or equal to 4)
Jiajia: (1-0.90) x + X + 20
Su Guo: first of all, the rounding of X / 100 is assumed to be y, then 16y + X
A total of 4 equations, draw coordinates 4 lines, through the intersection can see how appropriate consumption
Answer: buy refrigerator to Suguo supermarket, buy notebook to Jiajia supermarket

How to divide the scores of 1a, 2a, 3a, 1b, 2b and 3b in Guangdong college entrance examination?

First of all, 1a is one line, 2a is two lines, a 2b is two lines, B 3a is specialized a, 3b is specialized B, there is no 1b. After the college entrance examination every year, the Education Bureau will rank the candidates from high to low according to their scores, and then divide the batches according to a certain proportion. The score of the last candidate in a certain batch is the score line of the batch

At 9 a.m., there is a freight car driving from city a to city B at the speed of 49 kilometers per hour. At 11 a.m., there is another passenger car driving from city a to city B at the speed of 67 kilometers per hour. In order to drive safely, the distance between trains should not exceed 8 kilometers. When is the latest time for the freight car to stop?

It's about two hours ahead of time
Set X hour for truck parking
98+49X-8=67X
X=5
Stop at 16:00

What's three fifths plus six Sevens

51/35

A and B depart from a and B at the same time. For the first time, they meet 75 km away from A. after meeting, they continue to move forward and return to their destination. For the second time, they meet 55 km away from B. A and B are far away from each other______ Kilometers

75 × 3 = 225 (km), 225-55 = 170 (km)

Equation 2 - (2x + 4) / 3 = - (X-7) / 6 is obtained by removing the denominator

2 - (2x + 4) / 3 = - (X-7) / 6 multiply by 6 at the same time
12-2(2x+4)=-(x-7)
12-4x-8=-x+7
4x-x=12-8-7
3x=-3
x=-1