How to add and subtract decimals? It's agreed that there is a big reward

How to add and subtract decimals? It's agreed that there is a big reward

In the calculation, the number before the decimal point and the number after the decimal point are added / subtracted respectively
For example:
1.25+2.8=4.05
In the calculation note: 1 + 2 = 3, 0.25 + 0.8 = 1.05 two figures add up to get 4.05
So is subtraction

A workshop is in urgent need of 20 m ice cubes. It is known that the water has increased by 1 / 9 after freezing. Please calculate how many liters of water are needed to process these ice cubes

20 ／ (1 + 1 / 9) = 20 ／ 10 / 9 = 18 M3
18 m3 = 18000 L
It needs 18000 liters of water

1. () and 3:5 energy composition ratio
A. 10:6 B. one third: one fifth C. 30:50
2. () and 5:8 can form a ratio
A. One fifth: one eighth b.10:16 c.3:5
3. If x = three fourths y, then Y: x = ()
A. 4:3 B.1: three quarters c.3:4
4. In the following groups, the two ratios in group () can form a proportion
A. 25 C. 8:7 and 2:1.75 C
3. The ratio of the bottom diameter to the height of a cylinder is 4:7. It is known that the bottom diameter is 8cm, and how many cm is the height?

If x = three fourths of Y, then Y: x = (a) a.4:3 B.1: three fourths of c.3:44

The distance between port a and port B is 480 km. At 10 am, a cargo ship sails from port a to port B, and at 2 pm, a cargo ship sails from port B to Port A. after 12 hours, the passenger ship meets the cargo ship. The cargo ship travels 15 km per hour, and how many km per hour does the passenger ship travel?
Complete the equation according to the meaning of the question
The electrician team set up a transmission line with a total length of ~ m, 21% of the whole field was set up in 3 hours in the morning, and 280 km was set up in 1 hour with the same efficiency in the afternoon
=280*3
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1. It's a passenger ship in the morning
The departure time difference between the two ships is 4 hours
So when they met, the freighter drove for eight hours
（480-8*15）/12=30
2.280*3/（21/100）=4000

The two supermarkets brought in the same amount of milk. After supermarket a sold 45 cases and supermarket B sold 24 cases, the remaining 62.5% of supermarket B was supermarket A. how many cases of milk did the two supermarkets put in?

Formula
(45-24*62.5%)/(1-62.5%)
=30/37.5%
=80
equation
Each family has x boxes of milk
X-45=(X-24)*0.625
The solution is x = 80

Mathematics of grade 6 in primary school Volume 1
The total number of 5-yuan notes and 2-yuan notes is 200. It is known that the total value of 5-yuan notes is 160 yuan more than that of 2-yuan notes. How many of them are there?

160 △ 5 = 32 (sheets)
200-32 = 168 (sheets)
2 yuan: (168x5) / (5 + 2) = 120 (sheets)
5 yuan: 200-120 = 80 (sheets)

Integral addition and subtraction, seeking process and answer online====
(1) (X-Y) - (2x + 3Y) (2) (the second power of m-2mn) - 2 (the second power of M + the second power of 3mn-n)

Analysis: the key is to pay attention to the change of positive and negative signs when removing brackets, as well as the change of coefficients when merging similar terms. (1) (X-Y) - (2x + 3Y) = x-y-2x-3y = - x-4y (2) (the second power of m-2mn) - 2 (the second power of M + the second power of 3mn-n) = M & # 178; - 2mn-2m & # 178; - 6MN + 2n & # 178; = - M & #

Due to the different types of taxis in a city, the charging standards are also different. The starting price of type a taxis is 10 yuan (10 yuan within 3km) and 1.2 yuan after 3km. The starting price of type B taxis is 8 yuan (8 yuan within 3km) and 1.4 yuan per kilometer after 3km
(1) How much do you need to pay for a car and B car respectively for XKM (x > 3)
(2) If Lao Wang wants to take a taxi to a place 10km away, from the perspective of cost saving, which type of car should Lao Wang take?

(1) Type A: y = 10 + 1.2 (x-3)
Type B: y = 8 + 1.4 (x-3)
(2) Type A: y = 10 + 1.2 × (10-3)
＝10+8.4
= 18.4 yuan
Type B: y = 8 + 1.4 × (10-3)
＝8+9.8
= 17.8 yuan
17.8＜18.4
So Lao Wang should take type a car

The steps of integral addition and subtraction

This is similar to the order of the general four operations. If you have brackets, you should count the brackets first
However, the integral addition and subtraction method involves a calculation of merging similar terms
The method of merging the similar items is: in the similar items, the letter part remains unchanged, and the coefficients are added and subtracted
Definition of similar items: the same letters have the same index

1.(a^2b-ab)-(ab^2+ab)+2(ab^2+ba)
2.2(a^2-2ab)-3(-2/3a^2-ab)

1.(a^2b-ab)-(ab^2+ab)+2(ab^2+ba)
=a^2b-ab-ab^2-ab+2ab^2+2ab
=a^2b+ab^2
2.2(a^2-2ab)-3(-2/3a^2-ab)
=2a^2-4ab+2a^2+3ab
=4a^2+ab