The existing alloy of a and B metals is 10kg. If a few kilos of a metal are added, then B metal accounts for two parts and a metal accounts for three parts in this alloy. If a metal is doubled, then B metal accounts for three parts and a metal accounts for seven parts in this alloy. How much a metal is added for the first time? What is the percentage of a metal in this alloy?

Set: metal a x kg,
B metal y kg
First addition of metal a Z kg
Lie equation: x + y = 10
(X+Z)/Y=3/2
(X+2Z)/Y=7/3
The solution is x = 4, y = 6, z = 5

How to solve 3x & # 178; - 6x + 1 = 0 3x & # 178; - 5x = 152

First, 3x2-6x + 3 = 2, 3 (x-1) 2 = 2, (x-1) 2 = 2 / 3, X-1 = ± √ 2 / 3, x = 1 ± √ 2 / 3

Two engineering teams build the same road 250 meters a day. After 1000 meters, the second engineering team starts to build the road 300 meters a day. How many days after the second engineering team builds the road, the two engineering teams build the same number of meters

Suppose that after X days, the meters repaired by two engineering teams are equal
1000+250X=300X

4 / 5 △ 1 / 9 + 1 / 5 × 9

4 / 5 △ 1 / 9 + 1 / 5 × 9
=4 / 5 × 9 + 1 / 5 × 9
=9×(4/5+1/5)
=9

Xiao Cong and Xiao Ming have some glass balls. Xiao Cong says to Xiao Ming, "my glass balls are twice as big as yours." Xiao Ming says to Xiao Cong, "if you give me three, we'll have the same number." how many glass balls do they have?

According to the stem analysis, the number of Xiaoming's glass balls is 3 × 2 = 6, XiaoCong's glass balls is 6 × 2 = 12, a: XiaoCong has 12, Xiaoming has 6

Three continuous natural numbers, the middle number is a, the other two numbers are several and several

a-1,a+1

Xiaoming's house is on the sixth floor. He and his father started to play the game of "stone, scissors and cloth" from the fourth floor. It is stipulated that every time the winner can go up three steps, and the loser has to go down one step. After playing 20 times, father and Xiaoming both go from the fourth floor to the sixth floor. How many steps are there between the two floors?

There are 20 steps between the two floors

There is a rectangular sheet of iron 40 cm in length and 20 cm in width. Please use it to make a 5 cm deep rectangular sheet iron box without cover (welding joints are ignored). How many welding methods do you have? What is the maximum volume of the tin box you made?

As shown in the figure: (1) (40-5 × 2) × (20-5 × 2) × 5 = 30 × 10 × 5 = 1500 (ML); (2) (40-5) × (20-5 × 2) × 5 = 35 × 10 × 5 = 1750 (ML); (3) (40-5 × 4) × 20 × 5 = 20 × 20 × 5 = 2000 (ML); answer: there are three welding methods, and the maximum volume of the tin box is 2000 ml

It costs 1560 yuan to buy 18 tables and six chairs. The price of 10 tables is 680 yuan more than that of six chairs. How much are each table and chair

Do it with quadratic equation of two variables
Set a table x yuan, a chair y yuan
｛18x+6y=1560 （1）
10x-6y=680 （2）
The result of (1) + (2) is as follows:
28x=2240
x=80
Substituting x = 80 into (2) gives:
800-6y=680
6y=120
y=20
The solution of the original equations is {x = 80}
y=20
A: 80 yuan for each table and 20 yuan for each chair

5.04kg= Kilogram Gram 0.56 km= 6 m= 3.8 square meters=__ Square decimeter

The solution is (1) 5.04 kg = 5 kg 40 g; (2) 0.56 km = 560 m; (3) 0.6 hours = 36 min; (4) 3.8 square meters = 380 square decimeters