There are 500 students in the eighth grade, and 36 of them are selected to find the probability of a

In fact, it is very simple, first take out this student, that is, from 499 students, 35 students are drawn from the total number of drawings: c(499,35)=499! /35！

464！(35 of them!) *464！

The same is the denominator) and does not consider this student, and the number of the 36 students who are arbitrarily drawn from 500 students is total: c(500,36)=500! /36！

464！(36 of them!) *464！

is the same as the denominator) and then divide by the above two equations: c(499,35) c(500,36)= 36 500 = =

In addition, to tell you a little trick, in fact, "the probability of taking a specific 1 out of 2" is the same as "the probability of taking a specific 1 out of 500 out of 500", so "the probability of taking a specific 1 out of 500 out of 36" is also the same as "the probability of taking a specific 1 out of 500 out of 36".

Is this answer correct?

It's a combination problem, 500 people for 36 people all have the possibility of 500! /36！（500-36）！(1)

And all that is possible in the lottery is to put this person aside, and then choose 35 people out of the other 499 people, then it is 499! /35！（499-35）!(2)

And the probability of winning this person is (2) (1), which is about 36 500.

Summary. In stratified sampling, the probability of being drawn for boys and girls is equal, which is equal to the probability of each individual being drawn.

There are 800 female students in a school, and 300 of them are selected from 80 students, and the probability of drawing male students.

Stratified sampling? Right.

Okay, can you help me solve the true/false question, thank you.

Answer] The probability of drawing a boy is 1 in 10

Can you help me solve the true/false question, thank you.

In stratified sampling, the probability of being drawn for boys and girls is equal, which is equal to the probability of each individual being drawn.

1. The frequency of the fifth group

2. The number of people in the third group

3. The median falls within the 80-90 score range.

4. Number of students with good grades (

1) 1-

3) 80 to 90 fraction range, this is because

About 240 people.

(1) (2) people.

3) the median falls within 80-90 points, 4) (person.

Summary. Hello <>

According to the question, the probability of 2 students randomly selected from 200 8th graders to take the provincial test is: $ frac } frac div frac = frac$ Therefore, the probability that each student will be selected is $ frac$.

8.2 students were randomly selected from 200 eighth-grade students in a school to participate in the provincial test.

Hello [Flower Judgment Socks], according to the inscription, the probability of randomly selecting 2 students from 200 8th graders to participate in the provincial test is: $ frac } frac div frac = frac$ Therefore, the probability of each student being selected is $ frac$.

When calculating probabilities, it is necessary to clarify the total number of events that occurred and the number of favorable and dissimilar outcomes. For this problem, the total number of events is to select 2 students from 200 to participate in the provincial test, and the number of outcomes for the caller Sun is to choose any two students, so the number of favorable outcomes is $c $ When calculating the probability of the sum chain, the knowledge of permutations and combinations can be used to solve. At the same time, in practical application, it is necessary to pay attention to whether the conditions such as randomness and independence are met.

1. Mathematics scores of 50 students.

2. I didn't see you write it. Fill in the blank with ten strokes, a is 10 (and the total of your frequency should be 50 = =).

Three、..I don't understand what it means.

Fourth, 85 people.

Lots of mistakes. That's all I can do.

students' math scores.

The number of outstanding students of 40 is 12 40= then the number of outstanding students of 240 should be multiplied by 240, so the number of excellent students is 72.

A total of 240 students in the eighth grade of a school participated in a mathematics test, and the teacher randomly selected the results of 40 students for statistics, and a total of 12 students achieved excellent grades, and according to the above data, it is estimated that the number of students in the eighth grade of the school who achieved excellence in this mathematics test is about (72).

12/40……Among the 40 people who were drawn, 12 were excellent!