How to find the percentage of a number? Can frequency be regarded as the percentage?

How to find the percentage of a number? Can frequency be regarded as the percentage?

To find the percentage of a number is to divide it by the total number and multiply it by 100
Namely: quantity △ total number × 100 = percentage
Frequency is also known as relative times, that is, the number of times an event occurs is divided by the total number of events, that is, the number of times a data change occurs is removed by the total number of data in this group. Frequency is usually expressed in proportion or percentage. Therefore, when frequency is expressed in percentage, it can be regarded as percentage
May I help you!

I asked a question on Baidu two days ago
Suppose there are 30 numbers from 1 in the black box, and five numbers are given randomly. What is the probability of all the numbers being selected?
The answer given is p = 1 / (30c5) = 1 / 142506
But what I don't understand is:
C30 and 5, how to calculate 142506, C, is to look up the table, and is a fixed value or something? I just can't understand it here. So now I ask again, 30c5, how to calculate 142506?
And why is C (10,5) = 252 equal to 252?
In addition, if we say that C is a combinatorial number, is this combinatorial number to be multiplied or how?
For example, the combination number formula C (n, m), don't tell me to set the formula directly, don't give the result directly, I just don't understand the intermediate process!
I'll give you 30 points. First, if someone can make me understand,

C(n,m)=n!/m!/(n-m)!
C(30,5)=30!/5!/25!=30*29*28*27*26/(2*3*4*5)=142506

Production of a batch of parts, if everyone's work efficiency is the same, the number of participants and working hours into ()

The total amount of work has not changed, only work efficiency and time are multiplied

Work efficiency is certain, working hours and total amount of work___ ．

Because the total amount of work △ working time = working efficiency (certain), in line with the meaning of positive proportion, so the working efficiency is certain, the total amount of work and working time are in a positive proportion

When a worker completes a task and his work efficiency is increased by 25%, what is the percentage reduction in working hours

According to the relationship of workload = work efficiency * work time, it can be determined that the percentage of work time that can be reduced by completing this task is:
[1-1/（1+25/100)]*100%=20%

Efficiency calculation formula
Known electric power is 2200W, thermal power is 300W, what is the efficiency

2200/(300+2200)=0.88

For a batch of parts, it takes 8 hours for Party A to produce them alone. Now, after Party A has done it for 2 hours, Party B has joined in the work, and it takes 4 hours for them to complete the task. It takes Party B to produce these parts alone___ Hours

It takes 16 hours for Party B to finish this batch of parts alone

What are the specific types of fractional equation application problems, such as: work efficiency, etc

The application problems of fractional equation are widely combined with practice. The flexible use of the basic properties of fraction helps to solve the problems of fraction simplification, calculation and evaluation in application problems. The use of fraction calculation helps to solve practical problems in daily life

1. A ship sails between a and B along the Yangtze River. The downstream speed from a to B is 33 km / h, and the upstream speed from B to a is 27 km / h
2. From a to B, the waterway is nearly 40 km. At 10 a.m., a ship sails from a to B, and at 1 p.m., a car also sails from a to B, and they arrive at B at the same time. It is known that the speed of the ship is 24 km / h, and the speed of the car is 40 km / h

1. Let the distance between a and B be s, then
The time from a to B is: S / 33; the time from B to a is: S / 27
So the average speed of the ship is: 2S / [(s / 33) + (s / 27)] = 29.7 km / h
A: the average speed of the ship is 29.7 km / h
2. This problem is equivalent to the pursuit problem. The total pursuit distance of the car is: 24 * 3 + 40 = 112 km
So the driving time of the car is: 112 / (40-24) = 7 hours
So the travel time of the ship is: 7 + 3 = 10 hours
The waterway between a and B is: 24 * 10 = 240 km
The highway between a and B is 240 + 40 = 280 km or 40 * 7 = 280 km

It takes 24 days for Party A to do a job alone, and 16 days for Party B to do it alone. Now this job is done by Party A for one day, and then Party A and Party B cooperate. In the middle, Party A takes another day off. When they work again, the work efficiency of Party A and Party B increases by 20%. They work for another three days to complete the task, and ask Party A to have a rest on the next day

Party A and Party B worked together at the original speed for X days
The total amount of work is 1, the speed of a is 1 / 24, the speed of B is 1 / 16, the cooperation of a and B is 1 / 24 + 1 / 16 = 5 / 48
According to the working time column equation
1-1/24-(5/48)x-1/16-(5/48)*(1+1/5)*3=0
The solution is x = 5, that is to say, the second day to the sixth day is the day when Party A and Party B work together as soon as possible, so the seventh day is the day when Party A has a rest