Xiao Ming made a local call for six minutes, and then made a long-distance call. The total cost was 2.10 yuan. What's the talk time of the long-distance call 20 yuan for the first three minutes of a local call, and 0. 10 yuan for each subsequent call. 0

Set a long-distance call of X minutes, 10 seconds 0.1 yuan, 1 minute 0.6 yuan, X minutes 0.6x yuan,
0.6x + 0.1 (6-3) + 0.2 = 2.1 solution: x = 3
A: long distance call for 3 minutes
Welcome to inquire

An applied problem of Mathematical Engineering
Party A and Party B repair a batch of parts at the same time. Party A needs to repair 2 / 3 of that of Party B. Party A repairs 60 parts per hour and Party B repairs 80 parts per hour. When Party A finishes repairing, Party B still has 120 parts to repair. How many parts are there in total?

Suppose the total number is unit 5, then what a needs to complete is unit 2, and what B needs to complete is unit 3. When a completes unit 2, B completes unit 2 * 80 / 60 = 8 / 3, which is 3-3 / 8 = Unit 1 / 3120 / (1 / 3) = 360, which is unit 1, and the total number is unit 5, so 360 * 5 = 1800

Applied problems in Mathematical Engineering
It takes 15 days for team a to complete a project alone and 20 days for team B to complete it alone. After several days of cooperation between the two teams, team a was transferred to another task, and the rest was completed by team B in six days. How many days did the two teams cooperate?

Let a do x months, B do y months, the total amount of work as a unit of 1
Then there is a system of equations: X / 20 + Y / 30 = 1
160x+100y=3120 .②
The solution is x = 12, y = 12
So x: y = 1:1

Xiaoyu and Xiaoli went to the store to buy school supplies. Xiaoyu bought two ballpoint pens and two notebooks for 16 yuan, and Xiaoli bought three ballpoint pens and four notebooks for 29 yuan
2. After the final exam, the head teacher takes out the class fee of 100 yuan and gives it to the monitor to buy 24 ballpoint pens and notebooks as prizes. The notebooks are required to be no less than ballpoint pens, and several schemes are to be written one by one

The unit price of ballpoint pen is 3 yuan, and that of notebook is 5 yuan;
If x notebook is set, there will be;
x＞24-x;
2x＞24;
x＞12;
5x+3(24-x)≤100;
2x≤100-72;
2x≤28;
x≤14;
∴12＜x≤14;
There are two schemes: x = 13, 13 notebooks and 11 ballpoint pens;
X = 14, 14 notebooks, 10 ballpoint pens;

Xiaoyu and Xiaoli went to the store to buy school supplies. Xiaoyu bought two ballpoint pens and two notebooks for 16 yuan, and Xiaoli bought three ballpoint pens and one notebook for 29 yuan
1. What's the unit price of ballpoint pen and notebook?
2. After the final exam, the head teacher takes out the class fee of 100 yuan and gives it to the monitor to buy 24 ballpoint pens and notebooks as prizes. The notebooks are required to be no less than ballpoint pens, and several schemes are to be written one by one

Let the unit price of ballpoint pen and notebook be x and Y yuan respectively
2x+2y=16
3x+y=29
The solution is x = 10.5
y=-2.5
Is there a mistake in your question? How can the notebook get a negative number?

Xiao Li wants to use a compass to draw a circle with a circumference of 12.56 cm. Can you tell Li Li what is the distance between the two feet of the compass?

When you draw a circle with a compass, you can know that the distance between the two feet of the compass is the radius of the circle
According to the circumference formula of circle
Perimeter = 2 π R
R = 12.56 ﹣ 3.14 ﹣ 2 = 2cm

Xiao Li took some money to go shopping. She spent 8 yuan more than 2 / 5 of the money on her schoolbag. She spent 1 / 2 of the money on her paintbrush. At this time, there was 6 yuan left. How many yuan did Xiao Li take?

I can't read all the questions,

Xiaoli found a bag of desiccant in the biscuit box she just bought. She wanted to know the composition of the desiccant. So she took the desiccant to the laboratory, poured a small amount of desiccant into the beaker under the guidance of the teacher, added 10ml water, stirred it fully, let off heat, and got the turbid liquid. After filtration, she took a small amount of filtrate into the test tube, added phenolphthalein, the solution turned red, and then dropped a proper amount of people Dilute hydrochloric acid, red disappeared, but Yuan gas was formed. She took a small amount of filtrate and blew air into it. After a while, turbidity appeared. Xiao Li speculated that the main component of this package of desiccant was &Write out the chemical equation of the above change which belongs to the combination reaction ．

The desiccant dissolves in water and gives off heat. The product solution can make colorless phenolphthalein red, and the filtrate will become turbid when carbon dioxide is introduced. It can be inferred that the desiccant contains calcium oxide, which reacts with water to form calcium hydroxide. The chemical equation is Cao + H2 & nbsp; o = CA (OH) 2

Xiao Li's mother said to Xiao Li, "I've cleaned your schoolbag."
emergency

Xiao Li's mother said to Xiao Li that she had washed Xiao Li's schoolbag

The tour guide Xiao Zhang climbs a mountain in a scenic spot with a tour group
Halfway up the mountain, an old lady's clothes were cut by the thorns on the side of the road. She squatted there and didn't want to climb any more. The guide walked over and said to her with a smile: (). As soon as the old lady heard this, the sad cloud on her face disappeared and she went on climbing happily
Think about what the tour guide said

Old lady, you see the thorn is welcoming you in its way! You should be happy! You should not worry!

Xiao Ming made a local call for six minutes, and then made a long-distance call. The total cost was 2.10 yuan. What's the talk time of the long-distance call 20 yuan for the first three minutes of a local call, and 0. 10 yuan for each subsequent call. 0